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 $87.92   5.386%   $92.6554   $92.66   $92.65   $92.70  
  Purchase #2 $109.98   7.789%   $118.5463   $118.55   $118.55   $118.50  
  Purchase #3 $88.28   10.153%   $97.2431   $97.24   $97.25   $97.20  
  Purchase #4 $205.64   5.287%   $216.5122   $216.51   $216.50   $216.50  
  Purchase #5 $120.50   12.584%   $135.6637   $135.66   $135.65   $135.70  
  Purchase #6 $123.84   6.240%   $131.5676   $131.57   $131.55   $131.60  
  Purchase #7 $54.37   5.627%   $57.4294   $57.43   $57.45   $57.40  
  7 purchase totals = $790.53       $849.6177   $849.62   $849.60   $849.60