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 $62.42   10.546%   $69.0028   $69.00   $69.00   $69.00  
  Purchase #2 $142.37   9.611%   $156.0532   $156.05   $156.05   $156.10  
  Purchase #3 $79.83   11.232%   $88.7965   $88.80   $88.80   $88.80  
  Purchase #4 $8.57   7.523%   $9.2147   $9.21   $9.20   $9.20  
  Purchase #5 $215.74   7.596%   $232.1276   $232.13   $232.15   $232.10  
  Purchase #6 $152.29   13.747%   $173.2253   $173.23   $173.25   $173.20  
  Purchase #7 $22.45   4.543%   $23.4699   $23.47   $23.45   $23.50  
  7 purchase totals = $683.67       $751.8900   $751.89   $751.90   $751.90