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 $87.74   5.577%   $92.6333   $92.63   $92.65   $92.60  
  Purchase #2 $142.79   4.648%   $149.4269   $149.43   $149.45   $149.40  
  Purchase #3 $190.88   6.170%   $202.6573   $202.66   $202.65   $202.70  
  Purchase #4 $183.44   5.437%   $193.4136   $193.41   $193.40   $193.40  
  Purchase #5 $159.49   7.642%   $171.6782   $171.68   $171.70   $171.70  
  Purchase #6 $48.31   3.439%   $49.9714   $49.97   $49.95   $50.00  
  Purchase #7 $242.83   4.274%   $253.2086   $253.21   $253.20   $253.20  
  7 purchase totals = $1,055.48       $1,112.9893   $1,112.99   $1,113.00   $1,113.00