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 $30.86   7.140%   $33.0634   $33.06   $33.05   $33.10  
  Purchase #2 $245.46   4.641%   $256.8518   $256.85   $256.85   $256.90  
  Purchase #3 $62.34   5.562%   $65.8074   $65.81   $65.80   $65.80  
  Purchase #4 $207.97   11.720%   $232.3441   $232.34   $232.35   $232.30  
  Purchase #5 $155.90   10.330%   $172.0045   $172.00   $172.00   $172.00  
  Purchase #6 $234.93   4.591%   $245.7156   $245.72   $245.70   $245.70  
  Purchase #7 $122.64   10.336%   $135.3161   $135.32   $135.30   $135.30  
  7 purchase totals = $1,060.10       $1,141.1029   $1,141.10   $1,141.05   $1,141.10