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 $54.79   5.418%   $57.7585   $57.76   $57.75   $57.80  
  Purchase #2 $98.48   6.652%   $105.0309   $105.03   $105.05   $105.00  
  Purchase #3 $199.76   9.474%   $218.6853   $218.69   $218.70   $218.70  
  Purchase #4 $244.90   8.851%   $266.5761   $266.58   $266.60   $266.60  
  Purchase #5 $12.62   5.279%   $13.2862   $13.29   $13.30   $13.30  
  Purchase #6 $17.91   13.759%   $20.3742   $20.37   $20.35   $20.40  
  Purchase #7 $165.72   8.196%   $179.3024   $179.30   $179.30   $179.30  
  7 purchase totals = $794.18       $861.0136   $861.02   $861.05   $861.10