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 $39.84   11.326%   $44.3523   $44.35   $44.35   $44.40  
  Purchase #2 $188.99   8.414%   $204.8916   $204.89   $204.90   $204.90  
  Purchase #3 $118.40   9.701%   $129.886   $129.89   $129.90   $129.90  
  Purchase #4 $138.60   6.758%   $147.9666   $147.97   $147.95   $148.00  
  Purchase #5 $119.98   4.113%   $124.9148   $124.91   $124.90   $124.90  
  Purchase #6 $40.27   12.496%   $45.3021   $45.30   $45.30   $45.30  
  Purchase #7 $153.31   6.547%   $163.3472   $163.35   $163.35   $163.30  
  7 purchase totals = $799.39       $860.6606   $860.66   $860.65   $860.70