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 $32.69   6.151%   $34.7008   $34.70   $34.70   $34.70  
  Purchase #2 $53.49   6.689%   $57.0679   $57.07   $57.05   $57.10  
  Purchase #3 $73.39   11.320%   $81.6977   $81.70   $81.70   $81.70  
  Purchase #4 $226.88   7.689%   $244.3248   $244.32   $244.30   $244.30  
  Purchase #5 $192.72   4.331%   $201.0667   $201.07   $201.05   $201.10  
  Purchase #6 $66.70   12.387%   $74.9621   $74.96   $74.95   $75.00  
  Purchase #7 $95.93   3.454%   $99.2434   $99.24   $99.25   $99.20  
  7 purchase totals = $741.80       $793.0634   $793.06   $793.00   $793.10