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 $157.65   3.729%   $163.5288   $163.53   $163.55   $163.50  
  Purchase #2 $247.25   10.269%   $272.6401   $272.64   $272.65   $272.60  
  Purchase #3 $236.47   3.137%   $243.8881   $243.89   $243.90   $243.90  
  Purchase #4 $37.42   10.133%   $41.2118   $41.21   $41.20   $41.20  
  Purchase #5 $177.85   5.541%   $187.7047   $187.70   $187.70   $187.70  
  Purchase #6 $29.70   9.604%   $32.5524   $32.55   $32.55   $32.60  
  Purchase #7 $91.59   12.397%   $102.9444   $102.94   $102.95   $102.90  
  7 purchase totals = $977.93       $1,044.4703   $1,044.46   $1,044.50   $1,044.40