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 $55.37   10.738%   $61.3156   $61.32   $61.30   $61.30  
  Purchase #2 $144.97   13.734%   $164.8802   $164.88   $164.90   $164.90  
  Purchase #3 $43.47   6.263%   $46.1925   $46.19   $46.20   $46.20  
  Purchase #4 $205.77   6.734%   $219.6266   $219.63   $219.65   $219.60  
  Purchase #5 $235.66   4.648%   $246.6135   $246.61   $246.60   $246.60  
  Purchase #6 $151.59   7.270%   $162.6106   $162.61   $162.60   $162.60  
  Purchase #7 $158.94   11.366%   $177.0051   $177.01   $177.00   $177.00  
  7 purchase totals = $995.77       $1,078.2441   $1,078.25   $1,078.25   $1,078.20