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 $215.86   8.246%   $233.6598   $233.66   $233.65   $233.70  
  Purchase #2 $35.58   11.471%   $39.6614   $39.66   $39.65   $39.70  
  Purchase #3 $187.46   9.489%   $205.2481   $205.25   $205.25   $205.20  
  Purchase #4 $171.53   13.160%   $194.1033   $194.10   $194.10   $194.10  
  Purchase #5 $54.73   7.274%   $58.7111   $58.71   $58.70   $58.70  
  Purchase #6 $213.72   12.766%   $241.0035   $241.00   $241.00   $241.00  
  Purchase #7 $54.92   8.605%   $59.6459   $59.65   $59.65   $59.60  
  7 purchase totals = $933.80       $1,032.0331   $1,032.03   $1,032.00   $1,032.00