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 $56.55   9.609%   $61.9839   $61.98   $62.00   $62.00  
  Purchase #2 $23.31   4.642%   $24.3921   $24.39   $24.40   $24.40  
  Purchase #3 $221.55   10.574%   $244.9767   $244.98   $245.00   $245.00  
  Purchase #4 $76.56   7.668%   $82.4306   $82.43   $82.45   $82.40  
  Purchase #5 $195.30   11.723%   $218.195   $218.20   $218.20   $218.20  
  Purchase #6 $27.87   3.787%   $28.9254   $28.93   $28.95   $28.90  
  Purchase #7 $10.69   11.245%   $11.8921   $11.89   $11.90   $11.90  
  7 purchase totals = $611.83       $672.7958   $672.80   $672.90   $672.80