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 $11.59   10.813%   $12.8432   $12.84   $12.85   $12.80  
  Purchase #2 $31.80   7.354%   $34.1386   $34.14   $34.15   $34.10  
  Purchase #3 $163.94   3.265%   $169.2926   $169.29   $169.30   $169.30  
  Purchase #4 $201.65   3.145%   $207.9919   $207.99   $208.00   $208.00  
  Purchase #5 $239.61   4.571%   $250.5626   $250.56   $250.55   $250.60  
  Purchase #6 $207.47   12.213%   $232.8083   $232.81   $232.80   $232.80  
  Purchase #7 $96.82   7.531%   $104.1115   $104.11   $104.10   $104.10  
  7 purchase totals = $952.88       $1,011.7487   $1,011.74   $1,011.75   $1,011.70