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 $21.95   10.229%   $24.1953   $24.20   $24.20   $24.20  
  Purchase #2 $245.96   13.156%   $278.3185   $278.32   $278.30   $278.30  
  Purchase #3 $196.76   13.805%   $223.9227   $223.92   $223.90   $223.90  
  Purchase #4 $174.39   4.346%   $181.969   $181.97   $181.95   $182.00  
  Purchase #5 $194.90   3.107%   $200.9555   $200.96   $200.95   $201.00  
  Purchase #6 $12.26   6.582%   $13.067   $13.07   $13.05   $13.10  
  Purchase #7 $166.38   12.859%   $187.7748   $187.77   $187.75   $187.80  
  7 purchase totals = $1,012.60       $1,110.2028   $1,110.21   $1,110.10   $1,110.30