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 $184.82   6.466%   $196.7705   $196.77   $196.75   $196.80  
  Purchase #2 $14.29   5.632%   $15.0948   $15.09   $15.10   $15.10  
  Purchase #3 $164.38   7.489%   $176.6904   $176.69   $176.70   $176.70  
  Purchase #4 $22.37   11.500%   $24.9426   $24.94   $24.95   $24.90  
  Purchase #5 $124.62   5.802%   $131.8505   $131.85   $131.85   $131.90  
  Purchase #6 $203.98   6.165%   $216.5554   $216.56   $216.55   $216.60  
  Purchase #7 $112.99   11.621%   $126.1206   $126.12   $126.10   $126.10  
  7 purchase totals = $827.45       $888.0248   $888.02   $888.00   $888.10