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 $87.58   6.811%   $93.5451   $93.55   $93.55   $93.50  
  Purchase #2 $248.96   10.162%   $274.2593   $274.26   $274.25   $274.30  
  Purchase #3 $140.75   10.665%   $155.761   $155.76   $155.75   $155.80  
  Purchase #4 $13.41   13.836%   $15.2654   $15.27   $15.25   $15.30  
  Purchase #5 $101.64   9.113%   $110.9025   $110.90   $110.90   $110.90  
  Purchase #6 $168.56   9.207%   $184.0793   $184.08   $184.10   $184.10  
  Purchase #7 $171.86   12.244%   $192.9025   $192.90   $192.90   $192.90  
  7 purchase totals = $932.76       $1,026.7151   $1,026.72   $1,026.70   $1,026.80