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 $82.92   6.842%   $88.5934   $88.59   $88.60   $88.60  
  Purchase #2 $175.60   7.261%   $188.3503   $188.35   $188.35   $188.40  
  Purchase #3 $53.53   5.195%   $56.3109   $56.31   $56.30   $56.30  
  Purchase #4 $106.81   12.125%   $119.7607   $119.76   $119.75   $119.80  
  Purchase #5 $189.55   8.519%   $205.6978   $205.70   $205.70   $205.70  
  Purchase #6 $93.98   3.547%   $97.3135   $97.31   $97.30   $97.30  
  Purchase #7 $42.95   5.268%   $45.2126   $45.21   $45.20   $45.20  
  7 purchase totals = $745.34       $801.2392   $801.23   $801.20   $801.30