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 $187.80   8.593%   $203.9377   $203.94   $203.95   $203.90  
  Purchase #2 $38.53   5.433%   $40.6233   $40.62   $40.60   $40.60  
  Purchase #3 $93.60   5.262%   $98.5252   $98.53   $98.55   $98.50  
  Purchase #4 $229.72   5.494%   $242.3408   $242.34   $242.35   $242.30  
  Purchase #5 $53.36   11.548%   $59.522   $59.52   $59.50   $59.50  
  Purchase #6 $207.79   6.366%   $221.0179   $221.02   $221.00   $221.00  
  Purchase #7 $73.47   7.653%   $79.0927   $79.09   $79.10   $79.10  
  7 purchase totals = $884.27       $945.0596   $945.06   $945.05   $944.90