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 $68.26   11.159%   $75.8771   $75.88   $75.90   $75.90  
  Purchase #2 $118.69   13.204%   $134.3618   $134.36   $134.35   $134.40  
  Purchase #3 $148.62   12.603%   $167.3506   $167.35   $167.35   $167.40  
  Purchase #4 $9.68   6.295%   $10.2894   $10.29   $10.30   $10.30  
  Purchase #5 $233.70   7.725%   $251.7533   $251.75   $251.75   $251.80  
  Purchase #6 $197.98   11.339%   $220.429   $220.43   $220.45   $220.40  
  Purchase #7 $60.94   11.139%   $67.7281   $67.73   $67.75   $67.70  
  7 purchase totals = $837.87       $927.7893   $927.79   $927.85   $927.90