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 $100.77   9.498%   $110.3411   $110.34   $110.35   $110.30  
  Purchase #2 $180.28   4.776%   $188.8902   $188.89   $188.90   $188.90  
  Purchase #3 $31.38   13.400%   $35.5849   $35.58   $35.60   $35.60  
  Purchase #4 $13.45   11.765%   $15.0324   $15.03   $15.05   $15.00  
  Purchase #5 $238.50   12.305%   $267.8474   $267.85   $267.85   $267.80  
  Purchase #6 $236.81   12.837%   $267.2093   $267.21   $267.20   $267.20  
  Purchase #7 $230.61   10.476%   $254.7687   $254.77   $254.75   $254.80  
  7 purchase totals = $1,031.80       $1,139.6740   $1,139.67   $1,139.70   $1,139.60