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 $169.91   7.459%   $182.5836   $182.58   $182.60   $182.60  
  Purchase #2 $42.75   9.644%   $46.8728   $46.87   $46.85   $46.90  
  Purchase #3 $187.39   10.420%   $206.916   $206.92   $206.90   $206.90  
  Purchase #4 $149.37   13.225%   $169.1242   $169.12   $169.10   $169.10  
  Purchase #5 $54.52   13.120%   $61.673   $61.67   $61.65   $61.70  
  Purchase #6 $199.84   13.785%   $227.3879   $227.39   $227.40   $227.40  
  Purchase #7 $95.35   12.222%   $107.0037   $107.00   $107.00   $107.00  
  7 purchase totals = $899.13       $1,001.5612   $1,001.55   $1,001.50   $1,001.60