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 $185.66   9.111%   $202.5755   $202.58   $202.60   $202.60  
  Purchase #2 $12.41   13.720%   $14.1127   $14.11   $14.10   $14.10  
  Purchase #3 $94.56   10.590%   $104.5739   $104.57   $104.55   $104.60  
  Purchase #4 $34.77   6.688%   $37.0954   $37.10   $37.10   $37.10  
  Purchase #5 $184.32   9.422%   $201.6866   $201.69   $201.70   $201.70  
  Purchase #6 $76.50   6.107%   $81.1719   $81.17   $81.15   $81.20  
  Purchase #7 $94.66   12.713%   $106.6941   $106.69   $106.70   $106.70  
  7 purchase totals = $682.88       $747.9101   $747.91   $747.90   $748.00