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 $95.50   9.676%   $104.7406   $104.74   $104.75   $104.70  
  Purchase #2 $63.69   4.633%   $66.6408   $66.64   $66.65   $66.60  
  Purchase #3 $219.90   3.160%   $226.8488   $226.85   $226.85   $226.80  
  Purchase #4 $169.96   4.532%   $177.6626   $177.66   $177.65   $177.70  
  Purchase #5 $162.81   4.219%   $169.679   $169.68   $169.70   $169.70  
  Purchase #6 $215.85   8.506%   $234.2102   $234.21   $234.20   $234.20  
  Purchase #7 $111.93   12.629%   $126.0656   $126.07   $126.05   $126.10  
  7 purchase totals = $1,039.64       $1,105.8476   $1,105.85   $1,105.85   $1,105.80