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 $121.49   3.716%   $126.0046   $126.00   $126.00   $126.00  
  Purchase #2 $214.52   12.232%   $240.7601   $240.76   $240.75   $240.80  
  Purchase #3 $214.92   13.272%   $243.4442   $243.44   $243.45   $243.40  
  Purchase #4 $48.41   9.359%   $52.9407   $52.94   $52.95   $52.90  
  Purchase #5 $105.29   9.309%   $115.0914   $115.09   $115.10   $115.10  
  Purchase #6 $72.68   5.706%   $76.8271   $76.83   $76.85   $76.80  
  Purchase #7 $220.73   4.288%   $230.1949   $230.19   $230.20   $230.20  
  7 purchase totals = $998.04       $1,085.2630   $1,085.25   $1,085.30   $1,085.20