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 $61.96   5.808%   $65.5586   $65.56   $65.55   $65.60  
  Purchase #2 $87.69   13.124%   $99.1984   $99.20   $99.20   $99.20  
  Purchase #3 $151.30   13.658%   $171.9646   $171.96   $171.95   $172.00  
  Purchase #4 $99.94   7.124%   $107.0597   $107.06   $107.05   $107.10  
  Purchase #5 $220.83   7.767%   $237.9819   $237.98   $238.00   $238.00  
  Purchase #6 $169.57   5.420%   $178.7607   $178.76   $178.75   $178.80  
  Purchase #7 $140.39   12.372%   $157.7591   $157.76   $157.75   $157.80  
  7 purchase totals = $931.68       $1,018.2830   $1,018.28   $1,018.25   $1,018.50