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 $88.83   6.239%   $94.3721   $94.37   $94.35   $94.40  
  Purchase #2 $52.44   9.754%   $57.555   $57.56   $57.55   $57.60  
  Purchase #3 $158.88   6.233%   $168.783   $168.78   $168.80   $168.80  
  Purchase #4 $212.84   5.810%   $225.206   $225.21   $225.20   $225.20  
  Purchase #5 $202.91   3.256%   $209.5167   $209.52   $209.50   $209.50  
  Purchase #6 $203.36   8.747%   $221.1479   $221.15   $221.15   $221.10  
  Purchase #7 $234.96   11.579%   $262.166   $262.17   $262.15   $262.20  
  7 purchase totals = $1,154.22       $1,238.7467   $1,238.76   $1,238.70   $1,238.80