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 $13.73   3.792%   $14.2506   $14.25   $14.25   $14.30  
  Purchase #2 $93.73   11.278%   $104.3009   $104.30   $104.30   $104.30  
  Purchase #3 $55.33   9.460%   $60.5642   $60.56   $60.55   $60.60  
  Purchase #4 $49.84   7.738%   $53.6966   $53.70   $53.70   $53.70  
  Purchase #5 $242.41   3.657%   $251.2749   $251.27   $251.25   $251.30  
  Purchase #6 $221.73   6.500%   $236.1425   $236.14   $236.15   $236.10  
  Purchase #7 $57.85   12.603%   $65.1408   $65.14   $65.15   $65.10  
  7 purchase totals = $734.62       $785.3705   $785.36   $785.35   $785.40