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 $50.41   7.534%   $54.2079   $54.21   $54.20   $54.20  
  Purchase #2 $186.45   11.831%   $208.5089   $208.51   $208.50   $208.50  
  Purchase #3 $185.75   8.826%   $202.1443   $202.14   $202.15   $202.10  
  Purchase #4 $166.79   12.436%   $187.532   $187.53   $187.55   $187.50  
  Purchase #5 $16.41   3.146%   $16.9263   $16.93   $16.95   $16.90  
  Purchase #6 $88.27   9.107%   $96.3087   $96.31   $96.30   $96.30  
  Purchase #7 $11.57   3.412%   $11.9648   $11.96   $11.95   $12.00  
  7 purchase totals = $705.65       $777.5929   $777.59   $777.60   $777.50