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 $10.28   13.843%   $11.7031   $11.70   $11.70   $11.70  
  Purchase #2 $241.81   4.356%   $252.3432   $252.34   $252.35   $252.30  
  Purchase #3 $159.87   13.815%   $181.956   $181.96   $181.95   $182.00  
  Purchase #4 $156.48   13.261%   $177.2308   $177.23   $177.25   $177.20  
  Purchase #5 $215.79   9.447%   $236.1757   $236.18   $236.20   $236.20  
  Purchase #6 $58.72   3.783%   $60.9414   $60.94   $60.95   $60.90  
  Purchase #7 $221.78   13.156%   $250.9574   $250.96   $250.95   $251.00  
  7 purchase totals = $1,064.73       $1,171.3076   $1,171.31   $1,171.35   $1,171.30