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 $154.76   12.859%   $174.6606   $174.66   $174.65   $174.70  
  Purchase #2 $96.99   9.661%   $106.3602   $106.36   $106.35   $106.40  
  Purchase #3 $68.58   7.404%   $73.6577   $73.66   $73.65   $73.70  
  Purchase #4 $108.68   3.678%   $112.6773   $112.68   $112.70   $112.70  
  Purchase #5 $27.76   10.648%   $30.7159   $30.72   $30.70   $30.70  
  Purchase #6 $250.46   12.510%   $281.7925   $281.79   $281.80   $281.80  
  Purchase #7 $170.83   12.379%   $191.977   $191.98   $192.00   $192.00  
  7 purchase totals = $878.06       $971.8412   $971.85   $971.85   $972.00