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 $56.70   12.441%   $63.754   $63.75   $63.75   $63.80  
  Purchase #2 $219.91   7.225%   $235.7985   $235.80   $235.80   $235.80  
  Purchase #3 $37.79   8.186%   $40.8835   $40.88   $40.90   $40.90  
  Purchase #4 $187.54   3.261%   $193.6557   $193.66   $193.65   $193.70  
  Purchase #5 $211.53   8.250%   $228.9812   $228.98   $229.00   $229.00  
  Purchase #6 $204.58   11.586%   $228.2826   $228.28   $228.30   $228.30  
  Purchase #7 $33.64   5.272%   $35.4135   $35.41   $35.40   $35.40  
  7 purchase totals = $951.69       $1,026.7690   $1,026.76   $1,026.80   $1,026.90