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 $101.27   9.237%   $110.6243   $110.62   $110.60   $110.60  
  Purchase #2 $99.90   4.663%   $104.5583   $104.56   $104.55   $104.60  
  Purchase #3 $65.57   11.360%   $73.0188   $73.02   $73.00   $73.00  
  Purchase #4 $241.45   10.595%   $267.0316   $267.03   $267.05   $267.00  
  Purchase #5 $151.67   11.423%   $168.9953   $169.00   $169.00   $169.00  
  Purchase #6 $191.85   12.269%   $215.3881   $215.39   $215.40   $215.40  
  Purchase #7 $107.65   7.612%   $115.8443   $115.84   $115.85   $115.80  
  7 purchase totals = $959.36       $1,055.4607   $1,055.46   $1,055.45   $1,055.40