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 $24.92   6.715%   $26.5934   $26.59   $26.60   $26.60  
  Purchase #2 $71.98   5.640%   $76.0397   $76.04   $76.05   $76.00  
  Purchase #3 $24.33   10.793%   $26.9559   $26.96   $26.95   $27.00  
  Purchase #4 $218.68   5.731%   $231.2126   $231.21   $231.20   $231.20  
  Purchase #5 $204.27   13.625%   $232.1018   $232.10   $232.10   $232.10  
  Purchase #6 $227.75   10.404%   $251.4451   $251.45   $251.45   $251.40  
  Purchase #7 $219.33   10.399%   $242.1381   $242.14   $242.15   $242.10  
  7 purchase totals = $991.26       $1,086.4866   $1,086.49   $1,086.50   $1,086.40