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 $208.77   4.708%   $218.5989   $218.60   $218.60   $218.60  
  Purchase #2 $53.47   11.406%   $59.5688   $59.57   $59.55   $59.60  
  Purchase #3 $16.33   13.825%   $18.5876   $18.59   $18.60   $18.60  
  Purchase #4 $91.79   4.847%   $96.2391   $96.24   $96.25   $96.20  
  Purchase #5 $56.94   9.301%   $62.236   $62.24   $62.25   $62.20  
  Purchase #6 $11.67   10.710%   $12.9199   $12.92   $12.90   $12.90  
  Purchase #7 $201.29   5.750%   $212.8642   $212.86   $212.85   $212.90  
  7 purchase totals = $640.26       $681.0145   $681.02   $681.00   $681.00