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 $249.93   10.658%   $276.5675   $276.57   $276.55   $276.60  
  Purchase #2 $107.50   5.829%   $113.7662   $113.77   $113.75   $113.80  
  Purchase #3 $48.97   5.863%   $51.8411   $51.84   $51.85   $51.80  
  Purchase #4 $56.50   6.579%   $60.2171   $60.22   $60.20   $60.20  
  Purchase #5 $141.36   6.225%   $150.1597   $150.16   $150.15   $150.20  
  Purchase #6 $227.82   10.327%   $251.347   $251.35   $251.35   $251.30  
  Purchase #7 $32.29   5.195%   $33.9675   $33.97   $33.95   $34.00  
  7 purchase totals = $864.37       $937.8661   $937.88   $937.80   $937.90