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 $62.74   4.857%   $65.7873   $65.79   $65.80   $65.80  
  Purchase #2 $11.46   6.477%   $12.2023   $12.20   $12.20   $12.20  
  Purchase #3 $184.49   4.280%   $192.3862   $192.39   $192.40   $192.40  
  Purchase #4 $88.64   9.161%   $96.7603   $96.76   $96.75   $96.80  
  Purchase #5 $47.97   6.771%   $51.218   $51.22   $51.20   $51.20  
  Purchase #6 $126.67   8.294%   $137.176   $137.18   $137.20   $137.20  
  Purchase #7 $53.80   6.532%   $57.3142   $57.31   $57.30   $57.30  
  7 purchase totals = $575.77       $612.8443   $612.85   $612.85   $612.90