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 $163.52   7.383%   $175.5927   $175.59   $175.60   $175.60  
  Purchase #2 $117.82   9.403%   $128.8986   $128.90   $128.90   $128.90  
  Purchase #3 $205.86   6.133%   $218.4854   $218.49   $218.50   $218.50  
  Purchase #4 $66.33   12.501%   $74.6219   $74.62   $74.60   $74.60  
  Purchase #5 $133.96   12.611%   $150.8537   $150.85   $150.85   $150.90  
  Purchase #6 $125.75   3.309%   $129.9111   $129.91   $129.90   $129.90  
  Purchase #7 $139.79   7.739%   $150.6083   $150.61   $150.60   $150.60  
  7 purchase totals = $953.03       $1,028.9717   $1,028.97   $1,028.95   $1,029.00