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 $239.35   9.767%   $262.7273   $262.73   $262.75   $262.70  
  Purchase #2 $146.57   13.258%   $166.0023   $166.00   $166.00   $166.00  
  Purchase #3 $108.52   12.151%   $121.7063   $121.71   $121.70   $121.70  
  Purchase #4 $211.36   11.263%   $235.1655   $235.17   $235.15   $235.20  
  Purchase #5 $210.66   3.217%   $217.4369   $217.44   $217.45   $217.40  
  Purchase #6 $99.70   3.215%   $102.9054   $102.91   $102.90   $102.90  
  Purchase #7 $32.52   8.723%   $35.3567   $35.36   $35.35   $35.40  
  7 purchase totals = $1,048.68       $1,141.3004   $1,141.32   $1,141.30   $1,141.30