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 $52.76   8.215%   $57.0942   $57.09   $57.10   $57.10  
  Purchase #2 $192.81   4.834%   $202.1304   $202.13   $202.15   $202.10  
  Purchase #3 $27.68   13.132%   $31.3149   $31.31   $31.30   $31.30  
  Purchase #4 $92.49   4.591%   $96.7362   $96.74   $96.75   $96.70  
  Purchase #5 $209.66   8.230%   $226.915   $226.92   $226.90   $226.90  
  Purchase #6 $160.78   3.456%   $166.3366   $166.34   $166.35   $166.30  
  Purchase #7 $148.68   12.711%   $167.5787   $167.58   $167.60   $167.60  
  7 purchase totals = $884.86       $948.1060   $948.11   $948.15   $948.00