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 $63.45   7.301%   $68.0825   $68.08   $68.10   $68.10  
  Purchase #2 $67.89   11.332%   $75.5833   $75.58   $75.60   $75.60  
  Purchase #3 $58.71   9.455%   $64.261   $64.26   $64.25   $64.30  
  Purchase #4 $53.30   13.416%   $60.4507   $60.45   $60.45   $60.50  
  Purchase #5 $95.44   6.354%   $101.5043   $101.50   $101.50   $101.50  
  Purchase #6 $201.70   4.264%   $210.3005   $210.30   $210.30   $210.30  
  Purchase #7 $15.50   6.621%   $16.5263   $16.53   $16.55   $16.50  
  7 purchase totals = $555.99       $596.7086   $596.70   $596.75   $596.80