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 $56.94   12.253%   $63.9169   $63.92   $63.90   $63.90  
  Purchase #2 $188.32   11.165%   $209.3459   $209.35   $209.35   $209.30  
  Purchase #3 $138.59   11.297%   $154.2465   $154.25   $154.25   $154.20  
  Purchase #4 $202.90   4.495%   $212.0204   $212.02   $212.00   $212.00  
  Purchase #5 $26.88   10.813%   $29.7865   $29.79   $29.80   $29.80  
  Purchase #6 $157.43   6.102%   $167.0364   $167.04   $167.05   $167.00  
  Purchase #7 $230.86   4.659%   $241.6158   $241.62   $241.60   $241.60  
  7 purchase totals = $1,001.92       $1,077.9684   $1,077.99   $1,077.95   $1,077.80