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 $53.42   12.349%   $60.0168   $60.02   $60.00   $60.00  
  Purchase #2 $223.62   10.749%   $247.6569   $247.66   $247.65   $247.70  
  Purchase #3 $218.73   13.644%   $248.5735   $248.57   $248.55   $248.60  
  Purchase #4 $53.34   8.489%   $57.868   $57.87   $57.85   $57.90  
  Purchase #5 $104.48   3.629%   $108.2716   $108.27   $108.25   $108.30  
  Purchase #6 $94.78   9.538%   $103.8201   $103.82   $103.80   $103.80  
  Purchase #7 $133.44   5.102%   $140.2481   $140.25   $140.25   $140.20  
  7 purchase totals = $881.81       $966.4550   $966.46   $966.35   $966.50