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 $170.58   7.640%   $183.6123   $183.61   $183.60   $183.60  
  Purchase #2 $181.51   7.638%   $195.3737   $195.37   $195.35   $195.40  
  Purchase #3 $186.47   7.544%   $200.5373   $200.54   $200.55   $200.50  
  Purchase #4 $151.82   3.781%   $157.5603   $157.56   $157.55   $157.60  
  Purchase #5 $242.65   10.807%   $268.8732   $268.87   $268.85   $268.90  
  Purchase #6 $192.69   5.542%   $203.3689   $203.37   $203.35   $203.40  
  Purchase #7 $246.34   8.483%   $267.237   $267.24   $267.25   $267.20  
  7 purchase totals = $1,372.06       $1,476.5627   $1,476.56   $1,476.50   $1,476.60