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 $241.47   8.303%   $261.5193   $261.52   $261.50   $261.50  
  Purchase #2 $194.53   4.483%   $203.2508   $203.25   $203.25   $203.30  
  Purchase #3 $31.40   8.602%   $34.101   $34.10   $34.10   $34.10  
  Purchase #4 $159.39   3.258%   $164.5829   $164.58   $164.60   $164.60  
  Purchase #5 $84.33   10.175%   $92.9106   $92.91   $92.90   $92.90  
  Purchase #6 $246.54   10.477%   $272.37   $272.37   $272.35   $272.40  
  Purchase #7 $145.92   10.655%   $161.4678   $161.47   $161.45   $161.50  
  7 purchase totals = $1,103.58       $1,190.2024   $1,190.20   $1,190.15   $1,190.30