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 $201.66   10.590%   $223.0158   $223.02   $223.00   $223.00  
  Purchase #2 $113.29   3.222%   $116.9402   $116.94   $116.95   $116.90  
  Purchase #3 $45.29   13.365%   $51.343   $51.34   $51.35   $51.30  
  Purchase #4 $166.90   12.239%   $187.3269   $187.33   $187.35   $187.30  
  Purchase #5 $125.98   12.428%   $141.6368   $141.64   $141.65   $141.60  
  Purchase #6 $169.66   4.798%   $177.8003   $177.80   $177.80   $177.80  
  Purchase #7 $106.67   5.227%   $112.2456   $112.25   $112.25   $112.20  
  7 purchase totals = $929.45       $1,010.3086   $1,010.32   $1,010.35   $1,010.10