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 $215.96   9.641%   $236.7807   $236.78   $236.80   $236.80  
  Purchase #2 $211.92   11.760%   $236.8418   $236.84   $236.85   $236.80  
  Purchase #3 $91.70   11.112%   $101.8897   $101.89   $101.90   $101.90  
  Purchase #4 $173.47   4.605%   $181.4583   $181.46   $181.45   $181.50  
  Purchase #5 $163.32   7.358%   $175.3371   $175.34   $175.35   $175.30  
  Purchase #6 $53.41   6.460%   $56.8603   $56.86   $56.85   $56.90  
  Purchase #7 $238.96   5.737%   $252.6691   $252.67   $252.65   $252.70  
  7 purchase totals = $1,148.74       $1,241.8370   $1,241.84   $1,241.85   $1,241.90