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 $231.98   12.563%   $261.1236   $261.12   $261.10   $261.10  
  Purchase #2 $223.67   9.845%   $245.6903   $245.69   $245.70   $245.70  
  Purchase #3 $36.62   3.532%   $37.9134   $37.91   $37.90   $37.90  
  Purchase #4 $174.57   3.317%   $180.3605   $180.36   $180.35   $180.40  
  Purchase #5 $132.44   6.503%   $141.0526   $141.05   $141.05   $141.10  
  Purchase #6 $248.91   6.275%   $264.5291   $264.53   $264.55   $264.50  
  Purchase #7 $224.83   13.502%   $255.1865   $255.19   $255.20   $255.20  
  7 purchase totals = $1,273.02       $1,385.8560   $1,385.85   $1,385.85   $1,385.90