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 $93.46   7.596%   $100.5592   $100.56   $100.55   $100.60  
  Purchase #2 $212.76   8.339%   $230.5021   $230.50   $230.50   $230.50  
  Purchase #3 $62.88   13.331%   $71.2625   $71.26   $71.25   $71.30  
  Purchase #4 $224.89   9.497%   $246.2478   $246.25   $246.25   $246.20  
  Purchase #5 $157.85   10.556%   $174.5126   $174.51   $174.50   $174.50  
  Purchase #6 $53.52   10.165%   $58.9603   $58.96   $58.95   $59.00  
  Purchase #7 $159.62   5.868%   $168.9865   $168.99   $169.00   $169.00  
  7 purchase totals = $964.98       $1,051.0310   $1,051.03   $1,051.00   $1,051.10