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 $173.33   13.506%   $196.7399   $196.74   $196.75   $196.70  
  Purchase #2 $175.41   8.215%   $189.8199   $189.82   $189.80   $189.80  
  Purchase #3 $229.55   6.514%   $244.5029   $244.50   $244.50   $244.50  
  Purchase #4 $241.72   6.800%   $258.157   $258.16   $258.15   $258.20  
  Purchase #5 $12.89   8.415%   $13.9747   $13.97   $13.95   $14.00  
  Purchase #6 $161.59   4.175%   $168.3364   $168.34   $168.35   $168.30  
  Purchase #7 $216.85   6.634%   $231.2358   $231.24   $231.25   $231.20  
  7 purchase totals = $1,211.34       $1,302.7666   $1,302.77   $1,302.75   $1,302.70