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 $135.39   3.489%   $140.1138   $140.11   $140.10   $140.10  
  Purchase #2 $110.33   13.840%   $125.5997   $125.60   $125.60   $125.60  
  Purchase #3 $103.81   8.607%   $112.7449   $112.74   $112.75   $112.70  
  Purchase #4 $84.50   7.162%   $90.5519   $90.55   $90.55   $90.60  
  Purchase #5 $193.48   11.634%   $215.9895   $215.99   $216.00   $216.00  
  Purchase #6 $160.25   7.295%   $171.9402   $171.94   $171.95   $171.90  
  Purchase #7 $229.82   8.713%   $249.8442   $249.84   $249.85   $249.80  
  7 purchase totals = $1,017.58       $1,106.7842   $1,106.77   $1,106.80   $1,106.70