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 $63.81   3.419%   $65.9917   $65.99   $66.00   $66.00  
  Purchase #2 $219.53   9.600%   $240.6049   $240.60   $240.60   $240.60  
  Purchase #3 $118.55   12.754%   $133.6699   $133.67   $133.65   $133.70  
  Purchase #4 $123.34   11.438%   $137.4476   $137.45   $137.45   $137.40  
  Purchase #5 $103.99   12.222%   $116.6997   $116.70   $116.70   $116.70  
  Purchase #6 $41.72   9.796%   $45.8069   $45.81   $45.80   $45.80  
  Purchase #7 $164.72   11.444%   $183.5706   $183.57   $183.55   $183.60  
  7 purchase totals = $835.66       $923.7913   $923.79   $923.75   $923.80