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 $227.37   8.216%   $246.0507   $246.05   $246.05   $246.10  
  Purchase #2 $51.91   8.569%   $56.3582   $56.36   $56.35   $56.40  
  Purchase #3 $120.44   7.178%   $129.0852   $129.09   $129.10   $129.10  
  Purchase #4 $192.26   11.436%   $214.2469   $214.25   $214.25   $214.20  
  Purchase #5 $235.57   12.648%   $265.3649   $265.36   $265.35   $265.40  
  Purchase #6 $237.98   5.586%   $251.2736   $251.27   $251.25   $251.30  
  Purchase #7 $176.42   11.657%   $196.9853   $196.99   $197.00   $197.00  
  7 purchase totals = $1,241.95       $1,359.3648   $1,359.37   $1,359.35   $1,359.50