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 $48.83   7.638%   $52.5596   $52.56   $52.55   $52.60  
  Purchase #2 $155.36   13.124%   $175.7494   $175.75   $175.75   $175.70  
  Purchase #3 $16.76   9.868%   $18.4139   $18.41   $18.40   $18.40  
  Purchase #4 $198.86   7.619%   $214.0111   $214.01   $214.00   $214.00  
  Purchase #5 $174.85   12.835%   $197.292   $197.29   $197.30   $197.30  
  Purchase #6 $127.82   10.454%   $141.1823   $141.18   $141.20   $141.20  
  Purchase #7 $224.46   3.682%   $232.7246   $232.72   $232.70   $232.70  
  7 purchase totals = $946.94       $1,031.9329   $1,031.92   $1,031.90   $1,031.90