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 $63.40   10.450%   $70.0253   $70.03   $70.05   $70.00  
  Purchase #2 $224.55   13.118%   $254.0065   $254.01   $254.00   $254.00  
  Purchase #3 $21.37   4.620%   $22.3573   $22.36   $22.35   $22.40  
  Purchase #4 $226.58   12.458%   $254.8073   $254.81   $254.80   $254.80  
  Purchase #5 $67.44   12.375%   $75.7857   $75.79   $75.80   $75.80  
  Purchase #6 $164.86   8.103%   $178.2186   $178.22   $178.20   $178.20  
  Purchase #7 $234.80   9.669%   $257.5028   $257.50   $257.50   $257.50  
  7 purchase totals = $1,003.00       $1,112.7035   $1,112.72   $1,112.70   $1,112.70