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 $249.52   7.656%   $268.6233   $268.62   $268.60   $268.60  
  Purchase #2 $66.79   11.657%   $74.5757   $74.58   $74.60   $74.60  
  Purchase #3 $190.48   6.166%   $202.225   $202.23   $202.25   $202.20  
  Purchase #4 $203.28   9.823%   $223.2482   $223.25   $223.25   $223.20  
  Purchase #5 $194.87   8.841%   $212.0985   $212.10   $212.10   $212.10  
  Purchase #6 $204.95   7.664%   $220.6574   $220.66   $220.65   $220.70  
  Purchase #7 $241.55   8.304%   $261.6083   $261.61   $261.60   $261.60  
  7 purchase totals = $1,351.44       $1,463.0364   $1,463.05   $1,463.05   $1,463.00