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 $162.87   10.660%   $180.2319   $180.23   $180.25   $180.20  
  Purchase #2 $246.34   8.437%   $267.1237   $267.12   $267.10   $267.10  
  Purchase #3 $51.96   10.332%   $57.3285   $57.33   $57.35   $57.30  
  Purchase #4 $58.25   3.614%   $60.3552   $60.36   $60.35   $60.40  
  Purchase #5 $115.87   7.218%   $124.2335   $124.23   $124.25   $124.20  
  Purchase #6 $151.44   5.426%   $159.6571   $159.66   $159.65   $159.70  
  Purchase #7 $165.53   10.777%   $183.3692   $183.37   $183.35   $183.40  
  7 purchase totals = $952.26       $1,032.2991   $1,032.30   $1,032.30   $1,032.30