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 $245.59   9.618%   $269.2108   $269.21   $269.20   $269.20  
  Purchase #2 $183.58   3.135%   $189.3352   $189.34   $189.35   $189.30  
  Purchase #3 $14.49   12.466%   $16.2963   $16.30   $16.30   $16.30  
  Purchase #4 $47.50   5.648%   $50.1828   $50.18   $50.20   $50.20  
  Purchase #5 $190.36   3.605%   $197.2225   $197.22   $197.20   $197.20  
  Purchase #6 $103.88   12.684%   $117.0561   $117.06   $117.05   $117.10  
  Purchase #7 $169.62   9.821%   $186.2784   $186.28   $186.30   $186.30  
  7 purchase totals = $955.02       $1,025.5821   $1,025.59   $1,025.60   $1,025.60