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 $148.46   12.517%   $167.0427   $167.04   $167.05   $167.00  
  Purchase #2 $60.96   8.592%   $66.1977   $66.20   $66.20   $66.20  
  Purchase #3 $89.83   13.403%   $101.8699   $101.87   $101.85   $101.90  
  Purchase #4 $227.64   12.422%   $255.9174   $255.92   $255.90   $255.90  
  Purchase #5 $14.34   4.603%   $15.0001   $15.00   $15.00   $15.00  
  Purchase #6 $167.76   6.671%   $178.9513   $178.95   $178.95   $179.00  
  Purchase #7 $246.30   7.109%   $263.8095   $263.81   $263.80   $263.80  
  7 purchase totals = $955.29       $1,048.7886   $1,048.79   $1,048.75   $1,048.80