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 $24.65   8.478%   $26.7398   $26.74   $26.75   $26.70  
  Purchase #2 $66.57   6.823%   $71.1121   $71.11   $71.10   $71.10  
  Purchase #3 $74.97   13.391%   $85.0092   $85.01   $85.00   $85.00  
  Purchase #4 $243.85   7.252%   $261.534   $261.53   $261.55   $261.50  
  Purchase #5 $250.41   8.619%   $271.9928   $271.99   $272.00   $272.00  
  Purchase #6 $57.77   10.512%   $63.8428   $63.84   $63.85   $63.80  
  Purchase #7 $208.79   7.809%   $225.0944   $225.09   $225.10   $225.10  
  7 purchase totals = $927.01       $1,005.3251   $1,005.31   $1,005.35   $1,005.20