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 $165.91   6.452%   $176.6145   $176.61   $176.60   $176.60  
  Purchase #2 $220.59   11.346%   $245.6181   $245.62   $245.60   $245.60  
  Purchase #3 $42.65   9.778%   $46.8203   $46.82   $46.80   $46.80  
  Purchase #4 $204.49   13.788%   $232.6851   $232.69   $232.70   $232.70  
  Purchase #5 $153.89   6.335%   $163.6389   $163.64   $163.65   $163.60  
  Purchase #6 $124.65   11.731%   $139.2727   $139.27   $139.25   $139.30  
  Purchase #7 $234.34   12.682%   $264.059   $264.06   $264.05   $264.10  
  7 purchase totals = $1,146.52       $1,268.7086   $1,268.71   $1,268.65   $1,268.70