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 $66.59   6.170%   $70.6986   $70.70   $70.70   $70.70  
  Purchase #2 $190.55   13.649%   $216.5582   $216.56   $216.55   $216.60  
  Purchase #3 $219.61   7.602%   $236.3048   $236.30   $236.30   $236.30  
  Purchase #4 $65.57   12.834%   $73.9853   $73.99   $74.00   $74.00  
  Purchase #5 $134.78   9.606%   $147.727   $147.73   $147.75   $147.70  
  Purchase #6 $61.60   8.869%   $67.0633   $67.06   $67.05   $67.10  
  Purchase #7 $51.77   7.523%   $55.6647   $55.66   $55.65   $55.70  
  7 purchase totals = $790.47       $868.0019   $868.00   $868.00   $868.10