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 $61.59   11.747%   $68.825   $68.83   $68.85   $68.80  
  Purchase #2 $141.44   6.193%   $150.1994   $150.20   $150.20   $150.20  
  Purchase #3 $197.42   4.702%   $206.7027   $206.70   $206.70   $206.70  
  Purchase #4 $32.74   7.414%   $35.1673   $35.17   $35.15   $35.20  
  Purchase #5 $249.75   10.292%   $275.4543   $275.45   $275.45   $275.50  
  Purchase #6 $206.42   7.390%   $221.6744   $221.67   $221.65   $221.70  
  Purchase #7 $211.38   3.112%   $217.9581   $217.96   $217.95   $218.00  
  7 purchase totals = $1,100.74       $1,175.9812   $1,175.98   $1,175.95   $1,176.10