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 $52.83   6.397%   $56.2095   $56.21   $56.20   $56.20  
  Purchase #2 $76.95   11.320%   $85.6607   $85.66   $85.65   $85.70  
  Purchase #3 $220.38   10.604%   $243.7491   $243.75   $243.75   $243.70  
  Purchase #4 $170.37   6.446%   $181.3521   $181.35   $181.35   $181.40  
  Purchase #5 $126.73   12.604%   $142.703   $142.70   $142.70   $142.70  
  Purchase #6 $64.42   3.169%   $66.4615   $66.46   $66.45   $66.50  
  Purchase #7 $243.33   8.779%   $264.6919   $264.69   $264.70   $264.70  
  7 purchase totals = $955.01       $1,040.8278   $1,040.82   $1,040.80   $1,040.90