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 $85.51   8.442%   $92.7288   $92.73   $92.75   $92.70  
  Purchase #2 $25.90   10.513%   $28.6229   $28.62   $28.60   $28.60  
  Purchase #3 $170.63   13.655%   $193.9295   $193.93   $193.95   $193.90  
  Purchase #4 $199.81   3.255%   $206.3138   $206.31   $206.30   $206.30  
  Purchase #5 $176.77   4.197%   $184.189   $184.19   $184.20   $184.20  
  Purchase #6 $166.57   3.410%   $172.25   $172.25   $172.25   $172.30  
  Purchase #7 $204.68   3.375%   $211.588   $211.59   $211.60   $211.60  
  7 purchase totals = $1,029.87       $1,089.6220   $1,089.62   $1,089.65   $1,089.60