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 $203.93   10.671%   $225.6914   $225.69   $225.70   $225.70  
  Purchase #2 $6.35   8.647%   $6.8991   $6.90   $6.90   $6.90  
  Purchase #3 $60.63   11.806%   $67.788   $67.79   $67.80   $67.80  
  Purchase #4 $87.30   11.862%   $97.6555   $97.66   $97.65   $97.70  
  Purchase #5 $204.71   6.710%   $218.446   $218.45   $218.45   $218.40  
  Purchase #6 $243.35   4.304%   $253.8238   $253.82   $253.80   $253.80  
  Purchase #7 $17.96   6.553%   $19.1369   $19.14   $19.15   $19.10  
  7 purchase totals = $824.23       $889.4407   $889.45   $889.45   $889.40