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 $92.96   3.521%   $96.2331   $96.23   $96.25   $96.20  
  Purchase #2 $28.84   6.351%   $30.6716   $30.67   $30.65   $30.70  
  Purchase #3 $212.84   9.618%   $233.311   $233.31   $233.30   $233.30  
  Purchase #4 $109.63   7.244%   $117.5716   $117.57   $117.55   $117.60  
  Purchase #5 $247.70   5.780%   $262.0171   $262.02   $262.00   $262.00  
  Purchase #6 $157.77   5.533%   $166.4994   $166.50   $166.50   $166.50  
  Purchase #7 $249.74   4.487%   $260.9458   $260.95   $260.95   $260.90  
  7 purchase totals = $1,099.48       $1,167.2496   $1,167.25   $1,167.20   $1,167.20