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 $208.79   11.661%   $233.137   $233.14   $233.15   $233.10  
  Purchase #2 $143.64   8.578%   $155.9614   $155.96   $155.95   $156.00  
  Purchase #3 $102.32   6.502%   $108.9728   $108.97   $108.95   $109.00  
  Purchase #4 $244.39   9.450%   $267.4849   $267.48   $267.50   $267.50  
  Purchase #5 $94.88   13.335%   $107.5322   $107.53   $107.55   $107.50  
  Purchase #6 $156.46   10.681%   $173.1715   $173.17   $173.15   $173.20  
  Purchase #7 $162.47   10.794%   $180.007   $180.01   $180.00   $180.00  
  7 purchase totals = $1,112.95       $1,226.2668   $1,226.26   $1,226.25   $1,226.30