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 $80.59   7.579%   $86.6979   $86.70   $86.70   $86.70  
  Purchase #2 $195.75   12.573%   $220.3616   $220.36   $220.35   $220.40  
  Purchase #3 $32.66   13.764%   $37.1553   $37.16   $37.15   $37.20  
  Purchase #4 $152.41   12.627%   $171.6548   $171.65   $171.65   $171.70  
  Purchase #5 $197.32   12.857%   $222.6894   $222.69   $222.70   $222.70  
  Purchase #6 $163.74   13.384%   $185.655   $185.66   $185.65   $185.70  
  Purchase #7 $144.32   3.310%   $149.097   $149.10   $149.10   $149.10  
  7 purchase totals = $966.79       $1,073.3110   $1,073.32   $1,073.30   $1,073.50