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 $236.54   10.844%   $262.1904   $262.19   $262.20   $262.20  
  Purchase #2 $29.43   10.645%   $32.5628   $32.56   $32.55   $32.60  
  Purchase #3 $65.76   7.162%   $70.4697   $70.47   $70.45   $70.50  
  Purchase #4 $105.51   3.208%   $108.8948   $108.89   $108.90   $108.90  
  Purchase #5 $39.33   3.743%   $40.8021   $40.80   $40.80   $40.80  
  Purchase #6 $164.94   8.239%   $178.5294   $178.53   $178.55   $178.50  
  Purchase #7 $66.41   3.767%   $68.9117   $68.91   $68.90   $68.90  
  7 purchase totals = $707.92       $762.3609   $762.35   $762.35   $762.40