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 $222.90   7.808%   $240.304   $240.30   $240.30   $240.30  
  Purchase #2 $245.98   8.779%   $267.5746   $267.57   $267.55   $267.60  
  Purchase #3 $86.74   7.165%   $92.9549   $92.95   $92.95   $93.00  
  Purchase #4 $63.96   6.535%   $68.1398   $68.14   $68.15   $68.10  
  Purchase #5 $136.91   10.502%   $151.2883   $151.29   $151.30   $151.30  
  Purchase #6 $131.81   5.182%   $138.6404   $138.64   $138.65   $138.60  
  Purchase #7 $246.82   11.408%   $274.9772   $274.98   $275.00   $275.00  
  7 purchase totals = $1,135.12       $1,233.8792   $1,233.87   $1,233.90   $1,233.90