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 $31.84   7.826%   $34.3318   $34.33   $34.35   $34.30  
  Purchase #2 $171.58   13.432%   $194.6266   $194.63   $194.65   $194.60  
  Purchase #3 $52.26   12.114%   $58.5908   $58.59   $58.60   $58.60  
  Purchase #4 $34.41   9.239%   $37.5891   $37.59   $37.60   $37.60  
  Purchase #5 $94.67   7.429%   $101.703   $101.70   $101.70   $101.70  
  Purchase #6 $231.57   4.324%   $241.5831   $241.58   $241.60   $241.60  
  Purchase #7 $67.72   8.273%   $73.3225   $73.32   $73.30   $73.30  
  7 purchase totals = $684.05       $741.7469   $741.74   $741.80   $741.70