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 $32.63   12.656%   $36.7597   $36.76   $36.75   $36.80  
  Purchase #2 $220.87   4.406%   $230.6015   $230.60   $230.60   $230.60  
  Purchase #3 $199.27   10.471%   $220.1356   $220.14   $220.15   $220.10  
  Purchase #4 $59.62   3.768%   $61.8665   $61.87   $61.85   $61.90  
  Purchase #5 $93.60   13.836%   $106.5505   $106.55   $106.55   $106.60  
  Purchase #6 $143.68   9.118%   $156.7807   $156.78   $156.80   $156.80  
  Purchase #7 $184.96   3.700%   $191.8035   $191.80   $191.80   $191.80  
  7 purchase totals = $934.63       $1,004.4980   $1,004.50   $1,004.50   $1,004.60