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 $161.99   10.862%   $179.5854   $179.59   $179.60   $179.60  
  Purchase #2 $178.93   9.400%   $195.7494   $195.75   $195.75   $195.70  
  Purchase #3 $22.70   9.215%   $24.7918   $24.79   $24.80   $24.80  
  Purchase #4 $164.45   13.395%   $186.4781   $186.48   $186.50   $186.50  
  Purchase #5 $182.83   10.557%   $202.1314   $202.13   $202.15   $202.10  
  Purchase #6 $92.65   12.402%   $104.1405   $104.14   $104.15   $104.10  
  Purchase #7 $172.85   6.668%   $184.3756   $184.38   $184.40   $184.40  
  7 purchase totals = $976.40       $1,077.2522   $1,077.26   $1,077.35   $1,077.20