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 $98.54   4.121%   $102.6008   $102.60   $102.60   $102.60  
  Purchase #2 $81.33   13.826%   $92.5747   $92.57   $92.55   $92.60  
  Purchase #3 $185.43   10.484%   $204.8705   $204.87   $204.85   $204.90  
  Purchase #4 $153.97   11.785%   $172.1154   $172.12   $172.10   $172.10  
  Purchase #5 $124.83   8.106%   $134.9487   $134.95   $134.95   $134.90  
  Purchase #6 $59.28   11.287%   $65.9709   $65.97   $65.95   $66.00  
  Purchase #7 $241.39   3.729%   $250.3914   $250.39   $250.40   $250.40  
  7 purchase totals = $944.77       $1,023.4724   $1,023.47   $1,023.40   $1,023.50