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 $227.29   8.651%   $246.9529   $246.95   $246.95   $247.00  
  Purchase #2 $165.65   10.430%   $182.9273   $182.93   $182.95   $182.90  
  Purchase #3 $123.35   12.207%   $138.4073   $138.41   $138.40   $138.40  
  Purchase #4 $72.73   12.362%   $81.7209   $81.72   $81.70   $81.70  
  Purchase #5 $149.73   13.261%   $169.5857   $169.59   $169.60   $169.60  
  Purchase #6 $47.93   3.490%   $49.6028   $49.60   $49.60   $49.60  
  Purchase #7 $101.31   11.652%   $113.1146   $113.11   $113.10   $113.10  
  7 purchase totals = $887.99       $982.3115   $982.31   $982.30   $982.30