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 $45.46   4.702%   $47.5975   $47.60   $47.60   $47.60  
  Purchase #2 $52.31   7.613%   $56.2924   $56.29   $56.30   $56.30  
  Purchase #3 $187.69   6.573%   $200.0269   $200.03   $200.05   $200.00  
  Purchase #4 $182.61   3.682%   $189.3337   $189.33   $189.35   $189.30  
  Purchase #5 $60.44   5.867%   $63.986   $63.99   $64.00   $64.00  
  Purchase #6 $72.34   11.218%   $80.4551   $80.46   $80.45   $80.50  
  Purchase #7 $124.30   4.701%   $130.1433   $130.14   $130.15   $130.10  
  7 purchase totals = $725.15       $767.8349   $767.84   $767.90   $767.80