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 $162.57   4.758%   $170.3051   $170.31   $170.30   $170.30  
  Purchase #2 $141.32   4.468%   $147.6342   $147.63   $147.65   $147.60  
  Purchase #3 $58.73   6.462%   $62.5251   $62.53   $62.55   $62.50  
  Purchase #4 $19.35   7.862%   $20.8713   $20.87   $20.85   $20.90  
  Purchase #5 $196.64   9.169%   $214.6699   $214.67   $214.65   $214.70  
  Purchase #6 $118.39   12.675%   $133.3959   $133.40   $133.40   $133.40  
  Purchase #7 $240.65   6.497%   $256.285   $256.29   $256.30   $256.30  
  7 purchase totals = $937.65       $1,005.6865   $1,005.70   $1,005.70   $1,005.70