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 $72.70   11.623%   $81.1499   $81.15   $81.15   $81.10  
  Purchase #2 $192.59   7.811%   $207.6332   $207.63   $207.65   $207.60  
  Purchase #3 $112.64   7.266%   $120.8244   $120.82   $120.80   $120.80  
  Purchase #4 $189.73   9.359%   $207.4868   $207.49   $207.50   $207.50  
  Purchase #5 $39.68   4.747%   $41.5636   $41.56   $41.55   $41.60  
  Purchase #6 $224.27   12.769%   $252.907   $252.91   $252.90   $252.90  
  Purchase #7 $246.77   11.359%   $274.8006   $274.80   $274.80   $274.80  
  7 purchase totals = $1,078.38       $1,186.3655   $1,186.36   $1,186.35   $1,186.30