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 $110.57   8.186%   $119.6213   $119.62   $119.60   $119.60  
  Purchase #2 $156.84   12.336%   $176.1878   $176.19   $176.20   $176.20  
  Purchase #3 $182.45   12.336%   $204.957   $204.96   $204.95   $205.00  
  Purchase #4 $49.75   7.473%   $53.4678   $53.47   $53.45   $53.50  
  Purchase #5 $221.75   13.590%   $251.8858   $251.89   $251.90   $251.90  
  Purchase #6 $243.72   13.431%   $276.454   $276.45   $276.45   $276.50  
  Purchase #7 $65.58   8.337%   $71.0474   $71.05   $71.05   $71.00  
  7 purchase totals = $1,030.66       $1,153.6211   $1,153.63   $1,153.60   $1,153.70