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 $91.51   3.776%   $94.9654   $94.97   $94.95   $95.00  
  Purchase #2 $97.57   13.711%   $110.9478   $110.95   $110.95   $110.90  
  Purchase #3 $191.33   11.235%   $212.8259   $212.83   $212.85   $212.80  
  Purchase #4 $200.27   7.155%   $214.5993   $214.60   $214.60   $214.60  
  Purchase #5 $197.78   13.817%   $225.1073   $225.11   $225.10   $225.10  
  Purchase #6 $64.28   11.491%   $71.6664   $71.67   $71.65   $71.70  
  Purchase #7 $244.90   9.469%   $268.0896   $268.09   $268.10   $268.10  
  7 purchase totals = $1,087.64       $1,198.2017   $1,198.22   $1,198.20   $1,198.20