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 $30.89   10.226%   $34.0488   $34.05   $34.05   $34.00  
  Purchase #2 $175.78   5.803%   $185.9805   $185.98   $186.00   $186.00  
  Purchase #3 $167.52   9.581%   $183.5701   $183.57   $183.55   $183.60  
  Purchase #4 $237.34   10.395%   $262.0115   $262.01   $262.00   $262.00  
  Purchase #5 $186.67   3.828%   $193.8157   $193.82   $193.80   $193.80  
  Purchase #6 $236.26   6.359%   $251.2838   $251.28   $251.30   $251.30  
  Purchase #7 $163.98   4.157%   $170.7966   $170.80   $170.80   $170.80  
  7 purchase totals = $1,198.44       $1,281.5070   $1,281.51   $1,281.50   $1,281.50