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 $56.41   13.780%   $64.1833   $64.18   $64.20   $64.20  
  Purchase #2 $240.44   12.254%   $269.9035   $269.90   $269.90   $269.90  
  Purchase #3 $152.61   4.728%   $159.8254   $159.83   $159.85   $159.80  
  Purchase #4 $249.28   9.826%   $273.7743   $273.77   $273.75   $273.80  
  Purchase #5 $237.97   3.159%   $245.4875   $245.49   $245.50   $245.50  
  Purchase #6 $225.48   3.254%   $232.8171   $232.82   $232.80   $232.80  
  Purchase #7 $34.72   3.363%   $35.8876   $35.89   $35.90   $35.90  
  7 purchase totals = $1,196.91       $1,281.8787   $1,281.88   $1,281.90   $1,281.90