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 $105.61   10.150%   $116.3294   $116.33   $116.35   $116.30  
  Purchase #2 $221.39   10.208%   $243.9895   $243.99   $244.00   $244.00  
  Purchase #3 $80.70   7.277%   $86.5725   $86.57   $86.55   $86.60  
  Purchase #4 $79.91   9.540%   $87.5334   $87.53   $87.55   $87.50  
  Purchase #5 $217.74   13.771%   $247.725   $247.73   $247.75   $247.70  
  Purchase #6 $151.30   10.591%   $167.3242   $167.32   $167.30   $167.30  
  Purchase #7 $59.51   6.743%   $63.5228   $63.52   $63.50   $63.50  
  7 purchase totals = $916.16       $1,012.9968   $1,012.99   $1,013.00   $1,012.90