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 $84.77   10.759%   $93.8904   $93.89   $93.90   $93.90  
  Purchase #2 $250.36   7.740%   $269.7379   $269.74   $269.75   $269.70  
  Purchase #3 $37.26   3.808%   $38.6789   $38.68   $38.70   $38.70  
  Purchase #4 $174.93   10.540%   $193.3676   $193.37   $193.35   $193.40  
  Purchase #5 $83.33   13.729%   $94.7704   $94.77   $94.75   $94.80  
  Purchase #6 $156.92   12.171%   $176.0187   $176.02   $176.00   $176.00  
  Purchase #7 $91.33   5.309%   $96.1787   $96.18   $96.20   $96.20  
  7 purchase totals = $878.90       $962.6426   $962.65   $962.65   $962.70