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 $84.67   8.284%   $91.6841   $91.68   $91.70   $91.70  
  Purchase #2 $223.25   11.406%   $248.7139   $248.71   $248.70   $248.70  
  Purchase #3 $181.53   11.356%   $202.1445   $202.14   $202.15   $202.10  
  Purchase #4 $163.86   3.515%   $169.6197   $169.62   $169.60   $169.60  
  Purchase #5 $101.67   4.186%   $105.9259   $105.93   $105.95   $105.90  
  Purchase #6 $96.77   8.720%   $105.2083   $105.21   $105.20   $105.20  
  Purchase #7 $170.36   8.850%   $185.4369   $185.44   $185.45   $185.40  
  7 purchase totals = $1,022.11       $1,108.7333   $1,108.73   $1,108.75   $1,108.60