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 $168.73   5.388%   $177.8212   $177.82   $177.80   $177.80  
  Purchase #2 $220.96   9.434%   $241.8054   $241.81   $241.80   $241.80  
  Purchase #3 $23.46   9.802%   $25.7595   $25.76   $25.75   $25.80  
  Purchase #4 $126.85   3.390%   $131.1502   $131.15   $131.15   $131.20  
  Purchase #5 $112.47   5.162%   $118.2757   $118.28   $118.30   $118.30  
  Purchase #6 $244.56   9.580%   $267.9888   $267.99   $268.00   $268.00  
  Purchase #7 $224.52   7.141%   $240.553   $240.55   $240.55   $240.60  
  7 purchase totals = $1,121.55       $1,203.3538   $1,203.36   $1,203.35   $1,203.50