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 $166.51   7.615%   $179.1897   $179.19   $179.20   $179.20  
  Purchase #2 $231.87   6.230%   $246.3155   $246.32   $246.30   $246.30  
  Purchase #3 $193.72   4.644%   $202.7164   $202.72   $202.70   $202.70  
  Purchase #4 $234.46   7.580%   $252.2321   $252.23   $252.25   $252.20  
  Purchase #5 $100.57   5.263%   $105.863   $105.86   $105.85   $105.90  
  Purchase #6 $186.27   4.779%   $195.1718   $195.17   $195.15   $195.20  
  Purchase #7 $106.58   6.698%   $113.7187   $113.72   $113.70   $113.70  
  7 purchase totals = $1,219.98       $1,295.2072   $1,295.21   $1,295.15   $1,295.20