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 $14.51   3.710%   $15.0483   $15.05   $15.05   $15.00  
  Purchase #2 $247.49   11.398%   $275.6989   $275.70   $275.70   $275.70  
  Purchase #3 $31.79   8.620%   $34.5303   $34.53   $34.55   $34.50  
  Purchase #4 $246.83   13.653%   $280.5297   $280.53   $280.55   $280.50  
  Purchase #5 $33.44   6.568%   $35.6363   $35.64   $35.65   $35.60  
  Purchase #6 $199.38   9.775%   $218.8694   $218.87   $218.85   $218.90  
  Purchase #7 $201.87   5.502%   $212.9769   $212.98   $213.00   $213.00  
  7 purchase totals = $975.31       $1,073.2898   $1,073.30   $1,073.35   $1,073.20