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 $68.46   4.704%   $71.6804   $71.68   $71.70   $71.70  
  Purchase #2 $181.66   9.394%   $198.7251   $198.73   $198.75   $198.70  
  Purchase #3 $147.50   11.764%   $164.8519   $164.85   $164.85   $164.90  
  Purchase #4 $171.57   10.850%   $190.1853   $190.19   $190.20   $190.20  
  Purchase #5 $229.26   11.421%   $255.4438   $255.44   $255.45   $255.40  
  Purchase #6 $206.60   5.499%   $217.9609   $217.96   $217.95   $218.00  
  Purchase #7 $192.32   9.587%   $210.7577   $210.76   $210.75   $210.80  
  7 purchase totals = $1,197.37       $1,309.6051   $1,309.61   $1,309.65   $1,309.70