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 $189.48   13.548%   $215.1508   $215.15   $215.15   $215.20  
  Purchase #2 $186.76   9.706%   $204.8869   $204.89   $204.90   $204.90  
  Purchase #3 $17.94   7.208%   $19.2331   $19.23   $19.25   $19.20  
  Purchase #4 $32.27   9.347%   $35.2863   $35.29   $35.30   $35.30  
  Purchase #5 $239.84   10.198%   $264.2989   $264.30   $264.30   $264.30  
  Purchase #6 $102.46   4.256%   $106.8207   $106.82   $106.80   $106.80  
  Purchase #7 $156.43   13.371%   $177.3463   $177.35   $177.35   $177.30  
  7 purchase totals = $925.18       $1,023.0230   $1,023.03   $1,023.05   $1,023.00