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 $85.65   12.178%   $96.0805   $96.08   $96.10   $96.10  
  Purchase #2 $218.56   6.162%   $232.0277   $232.03   $232.05   $232.00  
  Purchase #3 $109.60   12.409%   $123.2003   $123.20   $123.20   $123.20  
  Purchase #4 $114.49   4.148%   $119.239   $119.24   $119.25   $119.20  
  Purchase #5 $226.47   8.472%   $245.6565   $245.66   $245.65   $245.70  
  Purchase #6 $237.44   5.694%   $250.9598   $250.96   $250.95   $251.00  
  Purchase #7 $148.60   12.646%   $167.392   $167.39   $167.40   $167.40  
  7 purchase totals = $1,140.81       $1,234.5558   $1,234.56   $1,234.60   $1,234.60