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 $84.54   9.740%   $92.7742   $92.77   $92.75   $92.80  
  Purchase #2 $43.50   5.696%   $45.9778   $45.98   $46.00   $46.00  
  Purchase #3 $233.85   10.154%   $257.5951   $257.60   $257.60   $257.60  
  Purchase #4 $12.73   10.698%   $14.0919   $14.09   $14.10   $14.10  
  Purchase #5 $147.75   11.531%   $164.7871   $164.79   $164.80   $164.80  
  Purchase #6 $212.75   11.501%   $237.2184   $237.22   $237.20   $237.20  
  Purchase #7 $106.75   6.709%   $113.9119   $113.91   $113.90   $113.90  
  7 purchase totals = $841.87       $926.3564   $926.36   $926.35   $926.40