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 $150.57   7.254%   $161.4923   $161.49   $161.50   $161.50  
  Purchase #2 $200.93   5.844%   $212.6723   $212.67   $212.65   $212.70  
  Purchase #3 $178.38   9.381%   $195.1138   $195.11   $195.10   $195.10  
  Purchase #4 $236.97   5.763%   $250.6266   $250.63   $250.65   $250.60  
  Purchase #5 $60.51   6.827%   $64.641   $64.64   $64.65   $64.60  
  Purchase #6 $177.97   8.738%   $193.521   $193.52   $193.50   $193.50  
  Purchase #7 $67.72   6.528%   $72.1408   $72.14   $72.15   $72.10  
  7 purchase totals = $1,073.05       $1,150.2078   $1,150.20   $1,150.20   $1,150.10