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 $222.85   5.462%   $235.0221   $235.02   $235.00   $235.00  
  Purchase #2 $91.81   11.523%   $102.3893   $102.39   $102.40   $102.40  
  Purchase #3 $14.89   13.779%   $16.9417   $16.94   $16.95   $16.90  
  Purchase #4 $189.63   4.601%   $198.3549   $198.35   $198.35   $198.40  
  Purchase #5 $103.44   3.572%   $107.1349   $107.13   $107.15   $107.10  
  Purchase #6 $182.25   3.110%   $187.918   $187.92   $187.90   $187.90  
  Purchase #7 $47.55   3.709%   $49.3136   $49.31   $49.30   $49.30  
  7 purchase totals = $852.42       $897.0745   $897.06   $897.05   $897.00