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 $126.69   8.538%   $137.5068   $137.51   $137.50   $137.50  
  Purchase #2 $83.80   13.172%   $94.8381   $94.84   $94.85   $94.80  
  Purchase #3 $93.99   10.651%   $104.0009   $104.00   $104.00   $104.00  
  Purchase #4 $132.56   12.557%   $149.2056   $149.21   $149.20   $149.20  
  Purchase #5 $216.62   12.508%   $243.7148   $243.71   $243.70   $243.70  
  Purchase #6 $242.52   6.816%   $259.0502   $259.05   $259.05   $259.10  
  Purchase #7 $24.86   4.754%   $26.0418   $26.04   $26.05   $26.00  
  7 purchase totals = $921.04       $1,014.3582   $1,014.36   $1,014.35   $1,014.30