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 $240.96   11.112%   $267.7355   $267.74   $267.75   $267.70  
  Purchase #2 $206.32   13.864%   $234.9242   $234.92   $234.90   $234.90  
  Purchase #3 $11.69   4.477%   $12.2134   $12.21   $12.20   $12.20  
  Purchase #4 $79.52   9.341%   $86.948   $86.95   $86.95   $86.90  
  Purchase #5 $196.83   5.266%   $207.1951   $207.20   $207.20   $207.20  
  Purchase #6 $79.26   9.612%   $86.8785   $86.88   $86.90   $86.90  
  Purchase #7 $195.43   3.779%   $202.8153   $202.82   $202.80   $202.80  
  7 purchase totals = $1,010.01       $1,098.7100   $1,098.72   $1,098.70   $1,098.60