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 $24.90   6.671%   $26.5611   $26.56   $26.55   $26.60  
  Purchase #2 $97.56   6.112%   $103.5229   $103.52   $103.50   $103.50  
  Purchase #3 $145.80   3.233%   $150.5137   $150.51   $150.50   $150.50  
  Purchase #4 $246.94   9.739%   $270.9895   $270.99   $271.00   $271.00  
  Purchase #5 $148.61   4.627%   $155.4862   $155.49   $155.50   $155.50  
  Purchase #6 $217.76   5.545%   $229.8348   $229.83   $229.85   $229.80  
  Purchase #7 $218.83   8.399%   $237.2095   $237.21   $237.20   $237.20  
  7 purchase totals = $1,100.40       $1,174.1177   $1,174.11   $1,174.10   $1,174.10