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 $240.86   9.187%   $262.9878   $262.99   $263.00   $263.00  
  Purchase #2 $194.89   12.802%   $219.8398   $219.84   $219.85   $219.80  
  Purchase #3 $61.33   4.854%   $64.307   $64.31   $64.30   $64.30  
  Purchase #4 $203.82   4.222%   $212.4253   $212.43   $212.45   $212.40  
  Purchase #5 $174.34   9.532%   $190.9581   $190.96   $190.95   $191.00  
  Purchase #6 $12.38   5.172%   $13.0203   $13.02   $13.00   $13.00  
  Purchase #7 $180.72   5.667%   $190.9614   $190.96   $190.95   $191.00  
  7 purchase totals = $1,068.34       $1,154.4997   $1,154.51   $1,154.50   $1,154.50