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 $12.94   3.826%   $13.4351   $13.44   $13.45   $13.40  
  Purchase #2 $52.81   6.402%   $56.1909   $56.19   $56.20   $56.20  
  Purchase #3 $180.90   13.803%   $205.8696   $205.87   $205.85   $205.90  
  Purchase #4 $214.61   5.244%   $225.8641   $225.86   $225.85   $225.90  
  Purchase #5 $81.51   13.699%   $92.6761   $92.68   $92.70   $92.70  
  Purchase #6 $189.85   9.136%   $207.1947   $207.19   $207.20   $207.20  
  Purchase #7 $218.84   11.235%   $243.4267   $243.43   $243.45   $243.40  
  7 purchase totals = $951.46       $1,044.6572   $1,044.66   $1,044.70   $1,044.70