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 $205.76   11.110%   $228.6199   $228.62   $228.60   $228.60  
  Purchase #2 $159.91   9.747%   $175.4964   $175.50   $175.50   $175.50  
  Purchase #3 $89.43   8.478%   $97.0119   $97.01   $97.00   $97.00  
  Purchase #4 $29.34   8.103%   $31.7174   $31.72   $31.70   $31.70  
  Purchase #5 $110.77   7.284%   $118.8385   $118.84   $118.85   $118.80  
  Purchase #6 $203.68   4.849%   $213.5564   $213.56   $213.55   $213.60  
  Purchase #7 $152.46   4.410%   $159.1835   $159.18   $159.20   $159.20  
  7 purchase totals = $951.35       $1,024.4240   $1,024.43   $1,024.40   $1,024.40