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 $194.52   6.565%   $207.2902   $207.29   $207.30   $207.30  
  Purchase #2 $216.62   5.552%   $228.6467   $228.65   $228.65   $228.60  
  Purchase #3 $36.36   10.182%   $40.0622   $40.06   $40.05   $40.10  
  Purchase #4 $185.62   7.119%   $198.8343   $198.83   $198.85   $198.80  
  Purchase #5 $74.61   11.152%   $82.9305   $82.93   $82.95   $82.90  
  Purchase #6 $18.96   4.613%   $19.8346   $19.83   $19.85   $19.80  
  Purchase #7 $31.93   5.120%   $33.5648   $33.56   $33.55   $33.60  
  7 purchase totals = $758.62       $811.1633   $811.15   $811.20   $811.10