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 $52.85   7.709%   $56.9242   $56.92   $56.90   $56.90  
  Purchase #2 $95.71   11.634%   $106.8449   $106.84   $106.85   $106.80  
  Purchase #3 $118.45   11.189%   $131.7034   $131.70   $131.70   $131.70  
  Purchase #4 $237.63   7.840%   $256.2602   $256.26   $256.25   $256.30  
  Purchase #5 $113.91   6.343%   $121.1353   $121.14   $121.15   $121.10  
  Purchase #6 $205.88   4.640%   $215.4328   $215.43   $215.45   $215.40  
  Purchase #7 $223.58   6.158%   $237.3481   $237.35   $237.35   $237.30  
  7 purchase totals = $1,048.01       $1,125.6489   $1,125.64   $1,125.65   $1,125.50