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 $242.99   7.731%   $261.7756   $261.78   $261.80   $261.80  
  Purchase #2 $106.35   11.268%   $118.3335   $118.33   $118.35   $118.30  
  Purchase #3 $89.39   5.213%   $94.0499   $94.05   $94.05   $94.00  
  Purchase #4 $201.79   5.835%   $213.5644   $213.56   $213.55   $213.60  
  Purchase #5 $126.98   13.171%   $143.7045   $143.70   $143.70   $143.70  
  Purchase #6 $77.83   5.551%   $82.1503   $82.15   $82.15   $82.20  
  Purchase #7 $32.64   5.396%   $34.4013   $34.40   $34.40   $34.40  
  7 purchase totals = $877.97       $947.9795   $947.97   $948.00   $948.00