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 $189.94   3.168%   $195.9573   $195.96   $195.95   $196.00  
  Purchase #2 $27.77   6.468%   $29.5662   $29.57   $29.55   $29.60  
  Purchase #3 $37.76   5.267%   $39.7488   $39.75   $39.75   $39.70  
  Purchase #4 $169.51   5.528%   $178.8805   $178.88   $178.90   $178.90  
  Purchase #5 $5.88   11.632%   $6.564   $6.56   $6.55   $6.60  
  Purchase #6 $66.64   11.712%   $74.4449   $74.44   $74.45   $74.40  
  Purchase #7 $206.58   6.642%   $220.301   $220.30   $220.30   $220.30  
  7 purchase totals = $704.08       $745.4627   $745.46   $745.45   $745.50