Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.64   13.618%   $243.8697   $243.87   $243.85   $243.90  
  Purchase #2 $132.68   9.414%   $145.1705   $145.17   $145.15   $145.20  
  Purchase #3 $184.62   8.295%   $199.9342   $199.93   $199.95   $199.90  
  Purchase #4 $234.89   7.785%   $253.1762   $253.18   $253.20   $253.20  
  Purchase #5 $244.98   4.449%   $255.8792   $255.88   $255.90   $255.90  
  Purchase #6 $111.79   12.178%   $125.4038   $125.40   $125.40   $125.40  
  Purchase #7 $203.44   3.349%   $210.2532   $210.25   $210.25   $210.30  
  7 purchase totals = $1,327.04       $1,433.6868   $1,433.68   $1,433.70   $1,433.80