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 $235.33   11.766%   $263.0189   $263.02   $263.00   $263.00  
  Purchase #2 $157.58   10.141%   $173.5602   $173.56   $173.55   $173.60  
  Purchase #3 $214.65   7.421%   $230.5792   $230.58   $230.60   $230.60  
  Purchase #4 $144.83   7.823%   $156.1601   $156.16   $156.15   $156.20  
  Purchase #5 $110.48   7.870%   $119.1748   $119.17   $119.15   $119.20  
  Purchase #6 $247.52   11.531%   $276.0615   $276.06   $276.05   $276.10  
  Purchase #7 $36.63   10.801%   $40.5864   $40.59   $40.60   $40.60  
  7 purchase totals = $1,147.02       $1,259.1411   $1,259.14   $1,259.10   $1,259.30