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 $141.34   10.337%   $155.9503   $155.95   $155.95   $156.00  
  Purchase #2 $223.82   10.734%   $247.8448   $247.84   $247.85   $247.80  
  Purchase #3 $175.87   7.647%   $189.3188   $189.32   $189.30   $189.30  
  Purchase #4 $95.63   13.841%   $108.8661   $108.87   $108.85   $108.90  
  Purchase #5 $159.65   10.217%   $175.9614   $175.96   $175.95   $176.00  
  Purchase #6 $45.51   3.318%   $47.02   $47.02   $47.00   $47.00  
  Purchase #7 $59.75   3.316%   $61.7313   $61.73   $61.75   $61.70  
  7 purchase totals = $901.57       $986.6927   $986.69   $986.65   $986.70