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 $61.38   10.806%   $68.0127   $68.01   $68.00   $68.00  
  Purchase #2 $238.35   11.581%   $265.9533   $265.95   $265.95   $266.00  
  Purchase #3 $220.99   8.286%   $239.3012   $239.30   $239.30   $239.30  
  Purchase #4 $68.68   7.427%   $73.7809   $73.78   $73.80   $73.80  
  Purchase #5 $97.33   10.512%   $107.5613   $107.56   $107.55   $107.60  
  Purchase #6 $137.40   9.147%   $149.968   $149.97   $149.95   $150.00  
  Purchase #7 $111.84   9.617%   $122.5957   $122.60   $122.60   $122.60  
  7 purchase totals = $935.97       $1,027.1731   $1,027.17   $1,027.15   $1,027.30