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 $12.48   12.628%   $14.056   $14.06   $14.05   $14.10  
  Purchase #2 $142.71   8.656%   $155.063   $155.06   $155.05   $155.10  
  Purchase #3 $206.93   7.180%   $221.7876   $221.79   $221.80   $221.80  
  Purchase #4 $62.87   6.221%   $66.7811   $66.78   $66.80   $66.80  
  Purchase #5 $46.54   12.338%   $52.2821   $52.28   $52.30   $52.30  
  Purchase #6 $237.86   12.213%   $266.9098   $266.91   $266.90   $266.90  
  Purchase #7 $225.98   6.732%   $241.193   $241.19   $241.20   $241.20  
  7 purchase totals = $935.37       $1,018.0726   $1,018.07   $1,018.10   $1,018.20