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 $78.79   11.709%   $88.0155   $88.02   $88.00   $88.00  
  Purchase #2 $71.32   11.109%   $79.2429   $79.24   $79.25   $79.20  
  Purchase #3 $43.40   7.487%   $46.6494   $46.65   $46.65   $46.60  
  Purchase #4 $250.43   7.799%   $269.961   $269.96   $269.95   $270.00  
  Purchase #5 $152.29   8.117%   $164.6514   $164.65   $164.65   $164.70  
  Purchase #6 $43.52   3.728%   $45.1424   $45.14   $45.15   $45.10  
  Purchase #7 $159.67   3.559%   $165.3527   $165.35   $165.35   $165.40  
  7 purchase totals = $799.42       $859.0153   $859.01   $859.00   $859.00