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 $184.62   12.310%   $207.3467   $207.35   $207.35   $207.30  
  Purchase #2 $100.64   4.191%   $104.8578   $104.86   $104.85   $104.90  
  Purchase #3 $174.50   8.253%   $188.9015   $188.90   $188.90   $188.90  
  Purchase #4 $58.47   12.861%   $65.9898   $65.99   $66.00   $66.00  
  Purchase #5 $128.56   13.851%   $146.3668   $146.37   $146.35   $146.40  
  Purchase #6 $86.75   9.469%   $94.9644   $94.96   $94.95   $95.00  
  Purchase #7 $222.39   9.648%   $243.8462   $243.85   $243.85   $243.80  
  7 purchase totals = $955.93       $1,052.2732   $1,052.28   $1,052.25   $1,052.30