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 $213.67   12.813%   $241.0475   $241.05   $241.05   $241.00  
  Purchase #2 $247.97   13.319%   $280.9971   $281.00   $281.00   $281.00  
  Purchase #3 $230.94   3.284%   $238.5241   $238.52   $238.50   $238.50  
  Purchase #4 $95.76   11.672%   $106.9371   $106.94   $106.95   $106.90  
  Purchase #5 $156.68   12.340%   $176.0143   $176.01   $176.00   $176.00  
  Purchase #6 $134.44   8.700%   $146.1363   $146.14   $146.15   $146.10  
  Purchase #7 $59.58   11.535%   $66.4526   $66.45   $66.45   $66.50  
  7 purchase totals = $1,139.04       $1,256.1090   $1,256.11   $1,256.10   $1,256.00