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 $144.35   6.466%   $153.6837   $153.68   $153.70   $153.70  
  Purchase #2 $228.40   10.636%   $252.6926   $252.69   $252.70   $252.70  
  Purchase #3 $235.43   9.209%   $257.1107   $257.11   $257.10   $257.10  
  Purchase #4 $151.57   8.702%   $164.7596   $164.76   $164.75   $164.80  
  Purchase #5 $41.58   7.641%   $44.7571   $44.76   $44.75   $44.80  
  Purchase #6 $91.84   4.710%   $96.1657   $96.17   $96.15   $96.20  
  Purchase #7 $102.69   5.606%   $108.4468   $108.45   $108.45   $108.40  
  7 purchase totals = $995.86       $1,077.6162   $1,077.62   $1,077.60   $1,077.70