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 $87.81   11.197%   $97.6421   $97.64   $97.65   $97.60  
  Purchase #2 $85.25   5.827%   $90.2175   $90.22   $90.20   $90.20  
  Purchase #3 $173.35   6.644%   $184.8674   $184.87   $184.85   $184.90  
  Purchase #4 $163.29   4.502%   $170.6413   $170.64   $170.65   $170.60  
  Purchase #5 $189.42   6.493%   $201.719   $201.72   $201.70   $201.70  
  Purchase #6 $94.70   10.346%   $104.4977   $104.50   $104.50   $104.50  
  Purchase #7 $87.59   5.677%   $92.5625   $92.56   $92.55   $92.60  
  7 purchase totals = $881.41       $942.1475   $942.15   $942.10   $942.10