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 $92.27   12.128%   $103.4605   $103.46   $103.45   $103.50  
  Purchase #2 $162.59   3.299%   $167.9538   $167.95   $167.95   $168.00  
  Purchase #3 $234.50   10.162%   $258.3299   $258.33   $258.35   $258.30  
  Purchase #4 $66.26   13.220%   $75.0196   $75.02   $75.00   $75.00  
  Purchase #5 $195.43   6.334%   $207.8085   $207.81   $207.80   $207.80  
  Purchase #6 $187.30   5.753%   $198.0754   $198.08   $198.10   $198.10  
  Purchase #7 $14.60   7.314%   $15.6678   $15.67   $15.65   $15.70  
  7 purchase totals = $952.95       $1,026.3155   $1,026.32   $1,026.30   $1,026.40