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 $183.64   11.416%   $204.6043   $204.60   $204.60   $204.60  
  Purchase #2 $178.54   7.499%   $191.9287   $191.93   $191.95   $191.90  
  Purchase #3 $219.84   4.669%   $230.1043   $230.10   $230.10   $230.10  
  Purchase #4 $160.77   11.477%   $179.2216   $179.22   $179.20   $179.20  
  Purchase #5 $233.48   13.479%   $264.9508   $264.95   $264.95   $265.00  
  Purchase #6 $193.38   11.675%   $215.9571   $215.96   $215.95   $216.00  
  Purchase #7 $224.57   4.142%   $233.8717   $233.87   $233.85   $233.90  
  7 purchase totals = $1,394.22       $1,520.6385   $1,520.63   $1,520.60   $1,520.70