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 $116.30   8.831%   $126.5705   $126.57   $126.55   $126.60  
  Purchase #2 $234.96   6.398%   $249.9927   $249.99   $250.00   $250.00  
  Purchase #3 $66.56   3.302%   $68.7578   $68.76   $68.75   $68.80  
  Purchase #4 $103.68   12.384%   $116.5197   $116.52   $116.50   $116.50  
  Purchase #5 $237.36   4.665%   $248.4328   $248.43   $248.45   $248.40  
  Purchase #6 $7.42   11.775%   $8.2937   $8.29   $8.30   $8.30  
  Purchase #7 $122.81   4.459%   $128.2861   $128.29   $128.30   $128.30  
  7 purchase totals = $889.09       $946.8533   $946.85   $946.85   $946.90