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 $162.58   7.118%   $174.1524   $174.15   $174.15   $174.20  
  Purchase #2 $96.64   13.297%   $109.4902   $109.49   $109.50   $109.50  
  Purchase #3 $175.89   12.392%   $197.6863   $197.69   $197.70   $197.70  
  Purchase #4 $179.92   12.569%   $202.5341   $202.53   $202.55   $202.50  
  Purchase #5 $21.88   12.517%   $24.6187   $24.62   $24.60   $24.60  
  Purchase #6 $220.28   8.594%   $239.2109   $239.21   $239.20   $239.20  
  Purchase #7 $88.75   4.247%   $92.5192   $92.52   $92.50   $92.50  
  7 purchase totals = $945.94       $1,040.2118   $1,040.21   $1,040.20   $1,040.20