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 $232.96   12.153%   $261.2716   $261.27   $261.25   $261.30  
  Purchase #2 $218.54   4.720%   $228.8551   $228.86   $228.85   $228.90  
  Purchase #3 $123.36   4.194%   $128.5337   $128.53   $128.55   $128.50  
  Purchase #4 $118.92   12.358%   $133.6161   $133.62   $133.60   $133.60  
  Purchase #5 $26.72   3.853%   $27.7495   $27.75   $27.75   $27.70  
  Purchase #6 $28.50   12.154%   $31.9639   $31.96   $31.95   $32.00  
  Purchase #7 $219.99   6.323%   $233.9   $233.90   $233.90   $233.90  
  7 purchase totals = $968.99       $1,045.8899   $1,045.89   $1,045.85   $1,045.90