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 $33.33   7.424%   $35.8044   $35.80   $35.80   $35.80  
  Purchase #2 $246.85   6.799%   $263.6333   $263.63   $263.65   $263.60  
  Purchase #3 $161.38   7.768%   $173.916   $173.92   $173.90   $173.90  
  Purchase #4 $185.26   3.266%   $191.3106   $191.31   $191.30   $191.30  
  Purchase #5 $239.80   4.790%   $251.2864   $251.29   $251.30   $251.30  
  Purchase #6 $204.35   5.516%   $215.6219   $215.62   $215.60   $215.60  
  Purchase #7 $126.68   3.780%   $131.4685   $131.47   $131.45   $131.50  
  7 purchase totals = $1,197.65       $1,263.0411   $1,263.04   $1,263.00   $1,263.00