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 $62.76   10.464%   $69.3272   $69.33   $69.35   $69.30  
  Purchase #2 $27.84   8.713%   $30.2657   $30.27   $30.25   $30.30  
  Purchase #3 $104.56   8.805%   $113.7665   $113.77   $113.75   $113.80  
  Purchase #4 $86.51   4.273%   $90.2066   $90.21   $90.20   $90.20  
  Purchase #5 $228.38   7.704%   $245.9744   $245.97   $245.95   $246.00  
  Purchase #6 $98.85   9.760%   $108.4978   $108.50   $108.50   $108.50  
  Purchase #7 $221.29   11.609%   $246.9796   $246.98   $247.00   $247.00  
  7 purchase totals = $830.19       $905.0178   $905.03   $905.00   $905.10