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 $219.76   11.493%   $245.017   $245.02   $245.00   $245.00  
  Purchase #2 $236.95   9.372%   $259.157   $259.16   $259.15   $259.20  
  Purchase #3 $243.98   12.131%   $273.5772   $273.58   $273.60   $273.60  
  Purchase #4 $225.53   4.107%   $234.7925   $234.79   $234.80   $234.80  
  Purchase #5 $14.72   4.433%   $15.3725   $15.37   $15.35   $15.40  
  Purchase #6 $109.31   9.385%   $119.5687   $119.57   $119.55   $119.60  
  Purchase #7 $225.64   12.124%   $252.9966   $253.00   $253.00   $253.00  
  7 purchase totals = $1,275.89       $1,400.4815   $1,400.49   $1,400.45   $1,400.60