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 $46.92   10.498%   $51.8457   $51.85   $51.85   $51.80  
  Purchase #2 $117.55   5.122%   $123.5709   $123.57   $123.55   $123.60  
  Purchase #3 $230.63   5.707%   $243.7921   $243.79   $243.80   $243.80  
  Purchase #4 $72.38   12.309%   $81.2893   $81.29   $81.30   $81.30  
  Purchase #5 $230.79   10.243%   $254.4298   $254.43   $254.45   $254.40  
  Purchase #6 $148.94   8.421%   $161.4822   $161.48   $161.50   $161.50  
  Purchase #7 $122.93   4.299%   $128.2148   $128.21   $128.20   $128.20  
  7 purchase totals = $970.14       $1,044.6248   $1,044.62   $1,044.65   $1,044.60