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 $102.91   11.343%   $114.5831   $114.58   $114.60   $114.60  
  Purchase #2 $53.63   13.280%   $60.7521   $60.75   $60.75   $60.80  
  Purchase #3 $109.27   10.651%   $120.9083   $120.91   $120.90   $120.90  
  Purchase #4 $207.26   7.615%   $223.0428   $223.04   $223.05   $223.00  
  Purchase #5 $46.70   12.306%   $52.4469   $52.45   $52.45   $52.40  
  Purchase #6 $149.97   8.227%   $162.308   $162.31   $162.30   $162.30  
  Purchase #7 $221.86   13.391%   $251.5693   $251.57   $251.55   $251.60  
  7 purchase totals = $891.60       $985.6105   $985.61   $985.60   $985.60