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 $182.75   10.689%   $202.2841   $202.28   $202.30   $202.30  
  Purchase #2 $133.34   9.149%   $145.5393   $145.54   $145.55   $145.50  
  Purchase #3 $87.55   11.190%   $97.3468   $97.35   $97.35   $97.30  
  Purchase #4 $211.78   6.789%   $226.1577   $226.16   $226.15   $226.20  
  Purchase #5 $23.41   7.718%   $25.2168   $25.22   $25.20   $25.20  
  Purchase #6 $213.68   7.637%   $229.9987   $230.00   $230.00   $230.00  
  Purchase #7 $69.66   8.217%   $75.384   $75.38   $75.40   $75.40  
  7 purchase totals = $922.17       $1,001.9274   $1,001.93   $1,001.95   $1,001.90