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 $174.35   9.644%   $191.1643   $191.16   $191.15   $191.20  
  Purchase #2 $244.75   12.518%   $275.3878   $275.39   $275.40   $275.40  
  Purchase #3 $23.89   3.397%   $24.7015   $24.70   $24.70   $24.70  
  Purchase #4 $90.61   7.433%   $97.345   $97.35   $97.35   $97.30  
  Purchase #5 $205.48   13.347%   $232.9054   $232.91   $232.90   $232.90  
  Purchase #6 $46.49   7.201%   $49.8377   $49.84   $49.85   $49.80  
  Purchase #7 $165.93   4.478%   $173.3603   $173.36   $173.35   $173.40  
  7 purchase totals = $951.50       $1,044.7020   $1,044.71   $1,044.70   $1,044.70