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 $66.87   6.699%   $71.3496   $71.35   $71.35   $71.30  
  Purchase #2 $28.71   12.423%   $32.2766   $32.28   $32.30   $32.30  
  Purchase #3 $248.77   13.838%   $283.1948   $283.19   $283.20   $283.20  
  Purchase #4 $144.65   7.659%   $155.7287   $155.73   $155.75   $155.70  
  Purchase #5 $68.75   10.578%   $76.0224   $76.02   $76.00   $76.00  
  Purchase #6 $245.92   9.367%   $268.9553   $268.96   $268.95   $269.00  
  Purchase #7 $202.42   7.325%   $217.2473   $217.25   $217.25   $217.20  
  7 purchase totals = $1,006.09       $1,104.7747   $1,104.78   $1,104.80   $1,104.70