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 $32.73   12.862%   $36.9397   $36.94   $36.95   $36.90  
  Purchase #2 $67.33   5.556%   $71.0709   $71.07   $71.05   $71.10  
  Purchase #3 $212.62   6.656%   $226.772   $226.77   $226.75   $226.80  
  Purchase #4 $200.65   6.490%   $213.6722   $213.67   $213.65   $213.70  
  Purchase #5 $34.54   3.297%   $35.6788   $35.68   $35.70   $35.70  
  Purchase #6 $35.47   11.277%   $39.47   $39.47   $39.45   $39.50  
  Purchase #7 $219.35   6.663%   $233.9653   $233.97   $233.95   $234.00  
  7 purchase totals = $802.69       $857.5689   $857.57   $857.50   $857.70