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 $52.77   13.539%   $59.9145   $59.91   $59.90   $59.90  
  Purchase #2 $31.71   10.192%   $34.9419   $34.94   $34.95   $34.90  
  Purchase #3 $148.77   5.812%   $157.4165   $157.42   $157.40   $157.40  
  Purchase #4 $42.74   11.521%   $47.6641   $47.66   $47.65   $47.70  
  Purchase #5 $138.46   4.342%   $144.4719   $144.47   $144.45   $144.50  
  Purchase #6 $218.69   9.128%   $238.652   $238.65   $238.65   $238.70  
  Purchase #7 $21.88   9.674%   $23.9967   $24.00   $24.00   $24.00  
  7 purchase totals = $655.02       $707.0576   $707.05   $707.00   $707.10