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 $154.41   8.121%   $166.9496   $166.95   $166.95   $166.90  
  Purchase #2 $232.83   8.661%   $252.9954   $253.00   $253.00   $253.00  
  Purchase #3 $201.40   7.467%   $216.4385   $216.44   $216.45   $216.40  
  Purchase #4 $190.87   11.359%   $212.5509   $212.55   $212.55   $212.60  
  Purchase #5 $83.70   7.278%   $89.7917   $89.79   $89.80   $89.80  
  Purchase #6 $141.61   11.308%   $157.6233   $157.62   $157.60   $157.60  
  Purchase #7 $107.97   12.794%   $121.7837   $121.78   $121.80   $121.80  
  7 purchase totals = $1,112.79       $1,218.1331   $1,218.13   $1,218.15   $1,218.10