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 $179.74   13.330%   $203.6993   $203.70   $203.70   $203.70  
  Purchase #2 $24.91   3.515%   $25.7856   $25.79   $25.80   $25.80  
  Purchase #3 $201.41   3.594%   $208.6487   $208.65   $208.65   $208.60  
  Purchase #4 $23.51   4.739%   $24.6241   $24.62   $24.60   $24.60  
  Purchase #5 $49.36   13.374%   $55.9614   $55.96   $55.95   $56.00  
  Purchase #6 $234.79   6.316%   $249.6193   $249.62   $249.60   $249.60  
  Purchase #7 $55.46   6.574%   $59.1059   $59.11   $59.10   $59.10  
  7 purchase totals = $769.18       $827.4443   $827.45   $827.40   $827.40