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 $152.81   10.204%   $168.4027   $168.40   $168.40   $168.40  
  Purchase #2 $194.66   8.717%   $211.6285   $211.63   $211.65   $211.60  
  Purchase #3 $17.59   3.235%   $18.159   $18.16   $18.15   $18.20  
  Purchase #4 $236.50   5.663%   $249.893   $249.89   $249.90   $249.90  
  Purchase #5 $108.77   11.174%   $120.924   $120.92   $120.90   $120.90  
  Purchase #6 $234.37   12.692%   $264.1162   $264.12   $264.10   $264.10  
  Purchase #7 $16.78   3.369%   $17.3453   $17.35   $17.35   $17.30  
  7 purchase totals = $961.48       $1,050.4687   $1,050.47   $1,050.45   $1,050.40