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 $218.46   12.631%   $246.0537   $246.05   $246.05   $246.10  
  Purchase #2 $49.58   4.686%   $51.9033   $51.90   $51.90   $51.90  
  Purchase #3 $61.36   11.663%   $68.5164   $68.52   $68.50   $68.50  
  Purchase #4 $30.36   3.722%   $31.49   $31.49   $31.50   $31.50  
  Purchase #5 $50.34   7.553%   $54.1422   $54.14   $54.15   $54.10  
  Purchase #6 $9.35   6.513%   $9.959   $9.96   $9.95   $10.00  
  Purchase #7 $216.34   7.497%   $232.559   $232.56   $232.55   $232.60  
  7 purchase totals = $635.79       $694.6236   $694.62   $694.60   $694.70