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 $50.48   6.153%   $53.586   $53.59   $53.60   $53.60  
  Purchase #2 $203.76   11.687%   $227.5734   $227.57   $227.55   $227.60  
  Purchase #3 $182.35   10.323%   $201.174   $201.17   $201.15   $201.20  
  Purchase #4 $64.34   3.753%   $66.7547   $66.75   $66.75   $66.80  
  Purchase #5 $71.77   11.259%   $79.8506   $79.85   $79.85   $79.90  
  Purchase #6 $81.56   12.408%   $91.68   $91.68   $91.70   $91.70  
  Purchase #7 $47.61   13.315%   $53.9493   $53.95   $53.95   $53.90  
  7 purchase totals = $701.87       $774.5680   $774.56   $774.55   $774.70