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 $75.67   12.664%   $85.2528   $85.25   $85.25   $85.30  
  Purchase #2 $73.57   5.527%   $77.6362   $77.64   $77.65   $77.60  
  Purchase #3 $102.54   11.136%   $113.9589   $113.96   $113.95   $114.00  
  Purchase #4 $24.29   12.438%   $27.3112   $27.31   $27.30   $27.30  
  Purchase #5 $118.94   9.865%   $130.6734   $130.67   $130.65   $130.70  
  Purchase #6 $197.49   6.612%   $210.548   $210.55   $210.55   $210.50  
  Purchase #7 $8.47   9.467%   $9.2719   $9.27   $9.25   $9.30  
  7 purchase totals = $600.97       $654.6524   $654.65   $654.60   $654.70