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 $104.32   12.692%   $117.5603   $117.56   $117.55   $117.60  
  Purchase #2 $229.51   11.217%   $255.2541   $255.25   $255.25   $255.30  
  Purchase #3 $62.94   9.166%   $68.7091   $68.71   $68.70   $68.70  
  Purchase #4 $226.59   5.286%   $238.5675   $238.57   $238.55   $238.60  
  Purchase #5 $240.94   10.639%   $266.5736   $266.57   $266.55   $266.60  
  Purchase #6 $14.52   13.339%   $16.4568   $16.46   $16.45   $16.50  
  Purchase #7 $72.46   6.539%   $77.1982   $77.20   $77.20   $77.20  
  7 purchase totals = $951.28       $1,040.3196   $1,040.32   $1,040.25   $1,040.50