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 $151.86   6.183%   $161.2495   $161.25   $161.25   $161.20  
  Purchase #2 $85.42   7.548%   $91.8675   $91.87   $91.85   $91.90  
  Purchase #3 $101.58   7.814%   $109.5175   $109.52   $109.50   $109.50  
  Purchase #4 $82.31   5.276%   $86.6527   $86.65   $86.65   $86.70  
  Purchase #5 $185.53   7.575%   $199.5839   $199.58   $199.60   $199.60  
  Purchase #6 $74.38   7.166%   $79.7101   $79.71   $79.70   $79.70  
  Purchase #7 $37.37   4.446%   $39.0315   $39.03   $39.05   $39.00  
  7 purchase totals = $718.45       $767.6127   $767.61   $767.60   $767.60