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 $147.62   13.455%   $167.4823   $167.48   $167.50   $167.50  
  Purchase #2 $241.71   10.787%   $267.7833   $267.78   $267.80   $267.80  
  Purchase #3 $157.78   10.825%   $174.8597   $174.86   $174.85   $174.90  
  Purchase #4 $129.99   10.141%   $143.1723   $143.17   $143.15   $143.20  
  Purchase #5 $60.82   5.226%   $63.9985   $64.00   $64.00   $64.00  
  Purchase #6 $91.43   5.525%   $96.4815   $96.48   $96.50   $96.50  
  Purchase #7 $139.95   10.207%   $154.2347   $154.23   $154.25   $154.20  
  7 purchase totals = $969.30       $1,068.0123   $1,068.00   $1,068.05   $1,068.10