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 $65.98   13.282%   $74.7435   $74.74   $74.75   $74.70  
  Purchase #2 $226.77   3.806%   $235.4009   $235.40   $235.40   $235.40  
  Purchase #3 $163.86   13.828%   $186.5186   $186.52   $186.50   $186.50  
  Purchase #4 $59.28   10.432%   $65.4641   $65.46   $65.45   $65.50  
  Purchase #5 $122.98   5.424%   $129.6504   $129.65   $129.65   $129.70  
  Purchase #6 $141.53   13.725%   $160.955   $160.96   $160.95   $161.00  
  Purchase #7 $216.86   13.348%   $245.8065   $245.81   $245.80   $245.80  
  7 purchase totals = $997.26       $1,098.5390   $1,098.54   $1,098.50   $1,098.60