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 $45.52   8.362%   $49.3264   $49.33   $49.35   $49.30  
  Purchase #2 $201.94   4.603%   $211.2353   $211.24   $211.25   $211.20  
  Purchase #3 $74.95   12.284%   $84.1569   $84.16   $84.15   $84.20  
  Purchase #4 $171.42   12.801%   $193.3635   $193.36   $193.35   $193.40  
  Purchase #5 $60.85   5.501%   $64.1974   $64.20   $64.20   $64.20  
  Purchase #6 $140.27   4.544%   $146.6439   $146.64   $146.65   $146.60  
  Purchase #7 $245.32   3.414%   $253.6952   $253.70   $253.70   $253.70  
  7 purchase totals = $940.27       $1,002.6186   $1,002.63   $1,002.65   $1,002.60