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 $202.31   8.433%   $219.3708   $219.37   $219.35   $219.40  
  Purchase #2 $26.81   13.255%   $30.3637   $30.36   $30.35   $30.40  
  Purchase #3 $73.59   13.803%   $83.7476   $83.75   $83.75   $83.70  
  Purchase #4 $120.86   9.595%   $132.4565   $132.46   $132.45   $132.50  
  Purchase #5 $159.90   4.391%   $166.9212   $166.92   $166.90   $166.90  
  Purchase #6 $195.90   6.607%   $208.8431   $208.84   $208.85   $208.80  
  Purchase #7 $202.66   11.730%   $226.432   $226.43   $226.45   $226.40  
  7 purchase totals = $982.03       $1,068.1349   $1,068.13   $1,068.10   $1,068.10