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 $71.31   7.538%   $76.6853   $76.69   $76.70   $76.70  
  Purchase #2 $248.82   7.595%   $267.7179   $267.72   $267.70   $267.70  
  Purchase #3 $235.48   3.228%   $243.0813   $243.08   $243.10   $243.10  
  Purchase #4 $49.78   5.358%   $52.4472   $52.45   $52.45   $52.40  
  Purchase #5 $250.45   10.348%   $276.3666   $276.37   $276.35   $276.40  
  Purchase #6 $24.46   4.183%   $25.4832   $25.48   $25.50   $25.50  
  Purchase #7 $93.61   6.120%   $99.3389   $99.34   $99.35   $99.30  
  7 purchase totals = $973.91       $1,041.1204   $1,041.13   $1,041.15   $1,041.10