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 $54.68   12.655%   $61.5998   $61.60   $61.60   $61.60  
  Purchase #2 $70.43   7.846%   $75.9559   $75.96   $75.95   $76.00  
  Purchase #3 $40.50   12.779%   $45.6755   $45.68   $45.70   $45.70  
  Purchase #4 $25.65   8.106%   $27.7292   $27.73   $27.75   $27.70  
  Purchase #5 $225.65   3.725%   $234.0555   $234.06   $234.05   $234.10  
  Purchase #6 $91.67   12.202%   $102.8556   $102.86   $102.85   $102.90  
  Purchase #7 $165.49   9.771%   $181.66   $181.66   $181.65   $181.70  
  7 purchase totals = $674.07       $729.5315   $729.55   $729.55   $729.70