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 $196.86   3.788%   $204.3171   $204.32   $204.30   $204.30  
  Purchase #2 $211.55   11.345%   $235.5503   $235.55   $235.55   $235.60  
  Purchase #3 $173.27   6.456%   $184.4563   $184.46   $184.45   $184.50  
  Purchase #4 $118.31   12.471%   $133.0644   $133.06   $133.05   $133.10  
  Purchase #5 $55.40   9.346%   $60.5777   $60.58   $60.60   $60.60  
  Purchase #6 $68.60   6.354%   $72.9588   $72.96   $72.95   $73.00  
  Purchase #7 $70.35   8.467%   $76.3065   $76.31   $76.30   $76.30  
  7 purchase totals = $894.34       $967.2311   $967.24   $967.20   $967.40