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 $169.94   9.211%   $185.5932   $185.59   $185.60   $185.60  
  Purchase #2 $131.49   13.573%   $149.3371   $149.34   $149.35   $149.30  
  Purchase #3 $68.98   3.169%   $71.166   $71.17   $71.15   $71.20  
  Purchase #4 $202.44   11.149%   $225.01   $225.01   $225.00   $225.00  
  Purchase #5 $123.65   7.106%   $132.4366   $132.44   $132.45   $132.40  
  Purchase #6 $53.69   8.633%   $58.3251   $58.33   $58.35   $58.30  
  Purchase #7 $209.46   8.396%   $227.0463   $227.05   $227.05   $227.00  
  7 purchase totals = $959.65       $1,048.9143   $1,048.93   $1,048.95   $1,048.80