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 $179.83   12.338%   $202.0174   $202.02   $202.00   $202.00  
  Purchase #2 $151.55   12.376%   $170.3058   $170.31   $170.30   $170.30  
  Purchase #3 $154.92   5.777%   $163.8697   $163.87   $163.85   $163.90  
  Purchase #4 $202.63   7.731%   $218.2953   $218.30   $218.30   $218.30  
  Purchase #5 $137.87   12.254%   $154.7646   $154.76   $154.75   $154.80  
  Purchase #6 $244.94   3.796%   $254.2379   $254.24   $254.25   $254.20  
  Purchase #7 $85.25   7.790%   $91.891   $91.89   $91.90   $91.90  
  7 purchase totals = $1,156.99       $1,255.3817   $1,255.39   $1,255.35   $1,255.40