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 $153.98   8.808%   $167.5426   $167.54   $167.55   $167.50  
  Purchase #2 $17.84   9.155%   $19.4733   $19.47   $19.45   $19.50  
  Purchase #3 $172.56   4.445%   $180.2303   $180.23   $180.25   $180.20  
  Purchase #4 $139.96   10.466%   $154.6082   $154.61   $154.60   $154.60  
  Purchase #5 $220.47   9.654%   $241.7542   $241.75   $241.75   $241.80  
  Purchase #6 $119.99   11.380%   $133.6449   $133.64   $133.65   $133.60  
  Purchase #7 $168.81   4.616%   $176.6023   $176.60   $176.60   $176.60  
  7 purchase totals = $993.61       $1,073.8558   $1,073.84   $1,073.85   $1,073.80