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 $108.95   12.677%   $122.7616   $122.76   $122.75   $122.80  
  Purchase #2 $242.72   3.692%   $251.6812   $251.68   $251.70   $251.70  
  Purchase #3 $155.95   8.450%   $169.1278   $169.13   $169.15   $169.10  
  Purchase #4 $124.90   5.709%   $132.0305   $132.03   $132.05   $132.00  
  Purchase #5 $59.45   6.589%   $63.3672   $63.37   $63.35   $63.40  
  Purchase #6 $187.44   4.793%   $196.424   $196.42   $196.40   $196.40  
  Purchase #7 $119.39   6.243%   $126.8435   $126.84   $126.85   $126.80  
  7 purchase totals = $998.80       $1,062.2358   $1,062.23   $1,062.25   $1,062.20