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 $183.41   5.554%   $193.5966   $193.60   $193.60   $193.60  
  Purchase #2 $95.68   3.309%   $98.8461   $98.85   $98.85   $98.80  
  Purchase #3 $50.91   4.830%   $53.369   $53.37   $53.35   $53.40  
  Purchase #4 $24.31   12.645%   $27.384   $27.38   $27.40   $27.40  
  Purchase #5 $241.39   12.211%   $270.8661   $270.87   $270.85   $270.90  
  Purchase #6 $153.41   11.858%   $171.6014   $171.60   $171.60   $171.60  
  Purchase #7 $7.81   13.147%   $8.8368   $8.84   $8.85   $8.80  
  7 purchase totals = $756.92       $824.5000   $824.51   $824.50   $824.50