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 $62.43   6.605%   $66.5535   $66.55   $66.55   $66.60  
  Purchase #2 $145.62   11.350%   $162.1479   $162.15   $162.15   $162.10  
  Purchase #3 $153.52   5.812%   $162.4426   $162.44   $162.45   $162.40  
  Purchase #4 $59.66   7.398%   $64.0736   $64.07   $64.05   $64.10  
  Purchase #5 $219.80   8.796%   $239.1336   $239.13   $239.15   $239.10  
  Purchase #6 $164.91   3.551%   $170.766   $170.77   $170.75   $170.80  
  Purchase #7 $50.93   7.629%   $54.8154   $54.82   $54.80   $54.80  
  7 purchase totals = $856.87       $919.9326   $919.93   $919.90   $919.90