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 $27.86   6.323%   $29.6216   $29.62   $29.60   $29.60  
  Purchase #2 $102.56   11.147%   $113.9924   $113.99   $114.00   $114.00  
  Purchase #3 $92.43   6.504%   $98.4416   $98.44   $98.45   $98.40  
  Purchase #4 $53.74   5.134%   $56.499   $56.50   $56.50   $56.50  
  Purchase #5 $214.73   7.423%   $230.6694   $230.67   $230.65   $230.70  
  Purchase #6 $100.98   13.372%   $114.483   $114.48   $114.50   $114.50  
  Purchase #7 $169.95   6.801%   $181.5083   $181.51   $181.50   $181.50  
  7 purchase totals = $762.25       $825.2153   $825.21   $825.20   $825.20