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 $185.57   4.114%   $193.2043   $193.20   $193.20   $193.20  
  Purchase #2 $141.57   11.155%   $157.3621   $157.36   $157.35   $157.40  
  Purchase #3 $150.70   12.525%   $169.5752   $169.58   $169.60   $169.60  
  Purchase #4 $39.30   8.804%   $42.76   $42.76   $42.75   $42.80  
  Purchase #5 $208.33   11.224%   $231.713   $231.71   $231.70   $231.70  
  Purchase #6 $242.52   10.563%   $268.1374   $268.14   $268.15   $268.10  
  Purchase #7 $61.29   6.629%   $65.3529   $65.35   $65.35   $65.40  
  7 purchase totals = $1,029.28       $1,128.1049   $1,128.10   $1,128.10   $1,128.20