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 $55.68   5.325%   $58.645   $58.65   $58.65   $58.60  
  Purchase #2 $51.41   7.558%   $55.2956   $55.30   $55.30   $55.30  
  Purchase #3 $134.93   8.202%   $145.997   $146.00   $146.00   $146.00  
  Purchase #4 $84.34   7.450%   $90.6233   $90.62   $90.60   $90.60  
  Purchase #5 $157.36   6.245%   $167.1871   $167.19   $167.20   $167.20  
  Purchase #6 $205.66   6.264%   $218.5425   $218.54   $218.55   $218.50  
  Purchase #7 $210.84   5.408%   $222.2422   $222.24   $222.25   $222.20  
  7 purchase totals = $900.22       $958.5327   $958.54   $958.55   $958.40