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 $124.26   6.201%   $131.9654   $131.97   $131.95   $132.00  
  Purchase #2 $126.63   12.304%   $142.2106   $142.21   $142.20   $142.20  
  Purchase #3 $204.90   7.388%   $220.038   $220.04   $220.05   $220.00  
  Purchase #4 $44.97   12.423%   $50.5566   $50.56   $50.55   $50.60  
  Purchase #5 $20.94   13.873%   $23.845   $23.85   $23.85   $23.80  
  Purchase #6 $28.64   13.623%   $32.5416   $32.54   $32.55   $32.50  
  Purchase #7 $163.60   11.243%   $181.9935   $181.99   $182.00   $182.00  
  7 purchase totals = $713.94       $783.1507   $783.16   $783.15   $783.10