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 $69.61   4.807%   $72.9562   $72.96   $72.95   $73.00  
  Purchase #2 $94.50   10.741%   $104.6502   $104.65   $104.65   $104.70  
  Purchase #3 $73.64   7.544%   $79.1954   $79.20   $79.20   $79.20  
  Purchase #4 $82.57   3.843%   $85.7432   $85.74   $85.75   $85.70  
  Purchase #5 $66.71   3.803%   $69.247   $69.25   $69.25   $69.20  
  Purchase #6 $78.59   11.115%   $87.3253   $87.33   $87.35   $87.30  
  Purchase #7 $201.41   5.819%   $213.13   $213.13   $213.15   $213.10  
  7 purchase totals = $667.03       $712.2473   $712.26   $712.30   $712.20