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 $53.62   10.234%   $59.1075   $59.11   $59.10   $59.10  
  Purchase #2 $104.73   10.129%   $115.3381   $115.34   $115.35   $115.30  
  Purchase #3 $68.92   6.256%   $73.2316   $73.23   $73.25   $73.20  
  Purchase #4 $190.39   6.656%   $203.0624   $203.06   $203.05   $203.10  
  Purchase #5 $127.58   10.685%   $141.2119   $141.21   $141.20   $141.20  
  Purchase #6 $20.34   3.658%   $21.084   $21.08   $21.10   $21.10  
  Purchase #7 $234.36   5.273%   $246.7178   $246.72   $246.70   $246.70  
  7 purchase totals = $799.94       $859.7533   $859.75   $859.75   $859.70