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 $191.35   5.160%   $201.2237   $201.22   $201.20   $201.20  
  Purchase #2 $17.51   7.416%   $18.8085   $18.81   $18.80   $18.80  
  Purchase #3 $47.53   13.453%   $53.9242   $53.92   $53.90   $53.90  
  Purchase #4 $5.65   13.118%   $6.3912   $6.39   $6.40   $6.40  
  Purchase #5 $183.41   5.576%   $193.6369   $193.64   $193.65   $193.60  
  Purchase #6 $38.48   6.799%   $41.0963   $41.10   $41.10   $41.10  
  Purchase #7 $242.67   6.297%   $257.9509   $257.95   $257.95   $258.00  
  7 purchase totals = $726.60       $773.0317   $773.03   $773.00   $773.00