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 $125.88   4.192%   $131.1569   $131.16   $131.15   $131.20  
  Purchase #2 $215.26   11.331%   $239.6511   $239.65   $239.65   $239.70  
  Purchase #3 $93.60   4.847%   $98.1368   $98.14   $98.15   $98.10  
  Purchase #4 $85.84   11.574%   $95.7751   $95.78   $95.80   $95.80  
  Purchase #5 $234.99   9.224%   $256.6655   $256.67   $256.65   $256.70  
  Purchase #6 $152.30   12.632%   $171.5385   $171.54   $171.55   $171.50  
  Purchase #7 $178.49   3.416%   $184.5872   $184.59   $184.60   $184.60  
  7 purchase totals = $1,086.36       $1,177.5111   $1,177.53   $1,177.55   $1,177.60