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 $58.87   9.533%   $64.4821   $64.48   $64.50   $64.50  
  Purchase #2 $176.47   3.672%   $182.95   $182.95   $182.95   $183.00  
  Purchase #3 $205.62   8.661%   $223.4287   $223.43   $223.45   $223.40  
  Purchase #4 $141.93   12.694%   $159.9466   $159.95   $159.95   $159.90  
  Purchase #5 $249.95   5.498%   $263.6923   $263.69   $263.70   $263.70  
  Purchase #6 $147.45   6.364%   $156.8337   $156.83   $156.85   $156.80  
  Purchase #7 $149.84   8.574%   $162.6873   $162.69   $162.70   $162.70  
  7 purchase totals = $1,130.13       $1,214.0207   $1,214.02   $1,214.10   $1,214.00