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 $223.28   8.244%   $241.6872   $241.69   $241.70   $241.70  
  Purchase #2 $161.94   3.686%   $167.9091   $167.91   $167.90   $167.90  
  Purchase #3 $109.52   4.411%   $114.3509   $114.35   $114.35   $114.40  
  Purchase #4 $234.69   13.343%   $266.0047   $266.00   $266.00   $266.00  
  Purchase #5 $212.65   9.726%   $233.3323   $233.33   $233.35   $233.30  
  Purchase #6 $102.97   12.609%   $115.9535   $115.95   $115.95   $116.00  
  Purchase #7 $77.43   8.339%   $83.8869   $83.89   $83.90   $83.90  
  7 purchase totals = $1,122.48       $1,223.1246   $1,223.12   $1,223.15   $1,223.20