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 $58.26   12.620%   $65.6124   $65.61   $65.60   $65.60  
  Purchase #2 $207.74   4.277%   $216.625   $216.63   $216.65   $216.60  
  Purchase #3 $139.37   6.142%   $147.9301   $147.93   $147.95   $147.90  
  Purchase #4 $118.42   5.318%   $124.7176   $124.72   $124.70   $124.70  
  Purchase #5 $136.82   6.740%   $146.0417   $146.04   $146.05   $146.00  
  Purchase #6 $110.60   6.268%   $117.5324   $117.53   $117.55   $117.50  
  Purchase #7 $189.25   8.157%   $204.6871   $204.69   $204.70   $204.70  
  7 purchase totals = $960.46       $1,023.1463   $1,023.15   $1,023.20   $1,023.00