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 $152.54   11.112%   $169.4902   $169.49   $169.50   $169.50  
  Purchase #2 $244.45   10.281%   $269.5819   $269.58   $269.60   $269.60  
  Purchase #3 $151.34   5.715%   $159.9891   $159.99   $160.00   $160.00  
  Purchase #4 $177.26   5.295%   $186.6459   $186.65   $186.65   $186.60  
  Purchase #5 $98.31   6.269%   $104.4731   $104.47   $104.45   $104.50  
  Purchase #6 $172.48   4.135%   $179.612   $179.61   $179.60   $179.60  
  Purchase #7 $62.81   3.286%   $64.8739   $64.87   $64.85   $64.90  
  7 purchase totals = $1,059.19       $1,134.6661   $1,134.66   $1,134.65   $1,134.70