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 $91.42   7.144%   $97.951   $97.95   $97.95   $98.00  
  Purchase #2 $226.86   6.172%   $240.8618   $240.86   $240.85   $240.90  
  Purchase #3 $195.95   7.818%   $211.2694   $211.27   $211.25   $211.30  
  Purchase #4 $147.57   7.199%   $158.1936   $158.19   $158.20   $158.20  
  Purchase #5 $130.94   10.556%   $144.762   $144.76   $144.75   $144.80  
  Purchase #6 $185.71   3.529%   $192.2637   $192.26   $192.25   $192.30  
  Purchase #7 $15.51   5.417%   $16.3502   $16.35   $16.35   $16.40  
  7 purchase totals = $993.96       $1,061.6517   $1,061.64   $1,061.60   $1,061.90