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 $213.79   6.242%   $227.1348   $227.13   $227.15   $227.10  
  Purchase #2 $235.57   8.494%   $255.5793   $255.58   $255.60   $255.60  
  Purchase #3 $154.49   8.363%   $167.41   $167.41   $167.40   $167.40  
  Purchase #4 $113.61   6.354%   $120.8288   $120.83   $120.85   $120.80  
  Purchase #5 $21.85   3.805%   $22.6814   $22.68   $22.70   $22.70  
  Purchase #6 $93.45   6.634%   $99.6495   $99.65   $99.65   $99.60  
  Purchase #7 $71.40   3.343%   $73.7869   $73.79   $73.80   $73.80  
  7 purchase totals = $904.16       $967.0707   $967.07   $967.15   $967.00