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 $245.65   5.843%   $260.0033   $260.00   $260.00   $260.00  
  Purchase #2 $89.89   4.465%   $93.9036   $93.90   $93.90   $93.90  
  Purchase #3 $92.57   12.436%   $104.082   $104.08   $104.10   $104.10  
  Purchase #4 $208.25   4.512%   $217.6462   $217.65   $217.65   $217.60  
  Purchase #5 $179.37   6.552%   $191.1223   $191.12   $191.10   $191.10  
  Purchase #6 $235.77   12.369%   $264.9324   $264.93   $264.95   $264.90  
  Purchase #7 $196.86   3.550%   $203.8485   $203.85   $203.85   $203.80  
  7 purchase totals = $1,248.36       $1,335.5383   $1,335.53   $1,335.55   $1,335.40