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 $26.71   3.681%   $27.6932   $27.69   $27.70   $27.70  
  Purchase #2 $177.67   9.172%   $193.9659   $193.97   $193.95   $194.00  
  Purchase #3 $245.57   10.428%   $271.178   $271.18   $271.20   $271.20  
  Purchase #4 $179.64   6.322%   $190.9968   $191.00   $191.00   $191.00  
  Purchase #5 $241.57   10.303%   $266.459   $266.46   $266.45   $266.50  
  Purchase #6 $111.79   9.145%   $122.0132   $122.01   $122.00   $122.00  
  Purchase #7 $83.89   11.856%   $93.836   $93.84   $93.85   $93.80  
  7 purchase totals = $1,066.84       $1,166.1421   $1,166.15   $1,166.15   $1,166.20