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 $137.70   11.717%   $153.8343   $153.83   $153.85   $153.80  
  Purchase #2 $101.25   12.259%   $113.6622   $113.66   $113.65   $113.70  
  Purchase #3 $119.47   5.463%   $125.9966   $126.00   $126.00   $126.00  
  Purchase #4 $233.93   5.496%   $246.7868   $246.79   $246.80   $246.80  
  Purchase #5 $156.69   5.843%   $165.8454   $165.85   $165.85   $165.80  
  Purchase #6 $23.26   11.803%   $26.0054   $26.01   $26.00   $26.00  
  Purchase #7 $248.46   7.103%   $266.1081   $266.11   $266.10   $266.10  
  7 purchase totals = $1,020.76       $1,098.2388   $1,098.25   $1,098.25   $1,098.20