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 $157.80   6.156%   $167.5142   $167.51   $167.50   $167.50  
  Purchase #2 $25.67   3.676%   $26.6136   $26.61   $26.60   $26.60  
  Purchase #3 $31.47   5.746%   $33.2783   $33.28   $33.30   $33.30  
  Purchase #4 $216.57   5.524%   $228.5333   $228.53   $228.55   $228.50  
  Purchase #5 $134.55   7.400%   $144.5067   $144.51   $144.50   $144.50  
  Purchase #6 $211.85   4.624%   $221.6459   $221.65   $221.65   $221.60  
  Purchase #7 $174.96   10.138%   $192.6974   $192.70   $192.70   $192.70  
  7 purchase totals = $952.87       $1,014.7894   $1,014.79   $1,014.80   $1,014.70