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 $217.52   4.651%   $227.6369   $227.64   $227.65   $227.60  
  Purchase #2 $97.72   9.632%   $107.1324   $107.13   $107.15   $107.10  
  Purchase #3 $181.54   10.726%   $201.012   $201.01   $201.00   $201.00  
  Purchase #4 $56.89   3.532%   $58.8994   $58.90   $58.90   $58.90  
  Purchase #5 $46.93   11.449%   $52.303   $52.30   $52.30   $52.30  
  Purchase #6 $22.62   13.244%   $25.6158   $25.62   $25.60   $25.60  
  Purchase #7 $79.58   7.292%   $85.383   $85.38   $85.40   $85.40  
  7 purchase totals = $702.80       $757.9825   $757.98   $758.00   $757.90