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 $105.74   12.544%   $119.004   $119.00   $119.00   $119.00  
  Purchase #2 $35.92   6.373%   $38.2092   $38.21   $38.20   $38.20  
  Purchase #3 $232.34   5.811%   $245.8413   $245.84   $245.85   $245.80  
  Purchase #4 $84.28   7.791%   $90.8463   $90.85   $90.85   $90.80  
  Purchase #5 $105.91   4.102%   $110.2544   $110.25   $110.25   $110.30  
  Purchase #6 $101.70   12.132%   $114.0382   $114.04   $114.05   $114.00  
  Purchase #7 $89.35   11.467%   $99.5958   $99.60   $99.60   $99.60  
  7 purchase totals = $755.24       $817.7892   $817.79   $817.80   $817.70