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 $190.71   6.509%   $203.1233   $203.12   $203.10   $203.10  
  Purchase #2 $195.44   10.276%   $215.5234   $215.52   $215.50   $215.50  
  Purchase #3 $45.83   10.594%   $50.6852   $50.69   $50.70   $50.70  
  Purchase #4 $216.42   3.541%   $224.0834   $224.08   $224.10   $224.10  
  Purchase #5 $182.86   6.186%   $194.1717   $194.17   $194.15   $194.20  
  Purchase #6 $187.44   3.562%   $194.1166   $194.12   $194.10   $194.10  
  Purchase #7 $175.78   11.294%   $195.6326   $195.63   $195.65   $195.60  
  7 purchase totals = $1,194.48       $1,277.3362   $1,277.33   $1,277.30   $1,277.30