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 $137.70   5.601%   $145.4126   $145.41   $145.40   $145.40  
  Purchase #2 $141.91   3.661%   $147.1053   $147.11   $147.10   $147.10  
  Purchase #3 $93.43   7.790%   $100.7082   $100.71   $100.70   $100.70  
  Purchase #4 $220.98   4.820%   $231.6312   $231.63   $231.65   $231.60  
  Purchase #5 $223.89   3.164%   $230.9739   $230.97   $230.95   $231.00  
  Purchase #6 $144.73   9.290%   $158.1754   $158.18   $158.20   $158.20  
  Purchase #7 $107.95   8.296%   $116.9055   $116.91   $116.90   $116.90  
  7 purchase totals = $1,070.59       $1,130.9121   $1,130.92   $1,130.90   $1,130.90