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 $88.27   7.274%   $94.6908   $94.69   $94.70   $94.70  
  Purchase #2 $41.87   12.186%   $46.9723   $46.97   $46.95   $47.00  
  Purchase #3 $237.32   3.732%   $246.1768   $246.18   $246.20   $246.20  
  Purchase #4 $77.35   4.441%   $80.7851   $80.79   $80.80   $80.80  
  Purchase #5 $38.80   8.442%   $42.0755   $42.08   $42.10   $42.10  
  Purchase #6 $55.68   9.836%   $61.1567   $61.16   $61.15   $61.20  
  Purchase #7 $245.69   6.788%   $262.3674   $262.37   $262.35   $262.40  
  7 purchase totals = $784.98       $834.2246   $834.24   $834.25   $834.40