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 $176.97   3.640%   $183.4117   $183.41   $183.40   $183.40  
  Purchase #2 $238.50   10.277%   $263.0106   $263.01   $263.00   $263.00  
  Purchase #3 $202.92   11.339%   $225.9291   $225.93   $225.95   $225.90  
  Purchase #4 $158.72   5.768%   $167.875   $167.88   $167.90   $167.90  
  Purchase #5 $218.91   3.249%   $226.0224   $226.02   $226.00   $226.00  
  Purchase #6 $50.57   9.658%   $55.4541   $55.45   $55.45   $55.50  
  Purchase #7 $220.51   3.350%   $227.8971   $227.90   $227.90   $227.90  
  7 purchase totals = $1,267.10       $1,349.6000   $1,349.60   $1,349.60   $1,349.60