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 $150.67   9.750%   $165.3603   $165.36   $165.35   $165.40  
  Purchase #2 $171.94   10.783%   $190.4803   $190.48   $190.50   $190.50  
  Purchase #3 $48.44   6.611%   $51.6424   $51.64   $51.65   $51.60  
  Purchase #4 $233.43   6.237%   $247.989   $247.99   $248.00   $248.00  
  Purchase #5 $40.74   12.830%   $45.9669   $45.97   $45.95   $46.00  
  Purchase #6 $235.50   12.102%   $264.0002   $264.00   $264.00   $264.00  
  Purchase #7 $95.51   3.146%   $98.5147   $98.51   $98.50   $98.50  
  7 purchase totals = $976.23       $1,063.9538   $1,063.95   $1,063.95   $1,064.00