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 $107.86   9.630%   $118.2469   $118.25   $118.25   $118.20  
  Purchase #2 $202.73   12.774%   $228.6267   $228.63   $228.65   $228.60  
  Purchase #3 $199.69   5.606%   $210.8846   $210.88   $210.90   $210.90  
  Purchase #4 $198.96   8.285%   $215.4438   $215.44   $215.45   $215.40  
  Purchase #5 $12.86   12.228%   $14.4325   $14.43   $14.45   $14.40  
  Purchase #6 $31.53   12.635%   $35.5138   $35.51   $35.50   $35.50  
  Purchase #7 $188.50   8.170%   $203.9005   $203.90   $203.90   $203.90  
  7 purchase totals = $942.13       $1,027.0488   $1,027.04   $1,027.10   $1,026.90