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 $5.29   13.624%   $6.0107   $6.01   $6.00   $6.00  
  Purchase #2 $249.40   8.104%   $269.6114   $269.61   $269.60   $269.60  
  Purchase #3 $74.59   11.491%   $83.1611   $83.16   $83.15   $83.20  
  Purchase #4 $243.91   10.120%   $268.5937   $268.59   $268.60   $268.60  
  Purchase #5 $246.52   3.581%   $255.3479   $255.35   $255.35   $255.30  
  Purchase #6 $192.46   3.581%   $199.352   $199.35   $199.35   $199.40  
  Purchase #7 $151.67   12.766%   $171.0322   $171.03   $171.05   $171.00  
  7 purchase totals = $1,163.84       $1,253.1090   $1,253.10   $1,253.10   $1,253.10