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 $131.70   12.453%   $148.1006   $148.10   $148.10   $148.10  
  Purchase #2 $119.88   5.455%   $126.4195   $126.42   $126.40   $126.40  
  Purchase #3 $158.42   11.831%   $177.1627   $177.16   $177.15   $177.20  
  Purchase #4 $71.52   8.493%   $77.5942   $77.59   $77.60   $77.60  
  Purchase #5 $246.82   9.483%   $270.2259   $270.23   $270.25   $270.20  
  Purchase #6 $188.40   8.739%   $204.8643   $204.86   $204.85   $204.90  
  Purchase #7 $181.26   6.165%   $192.4347   $192.43   $192.45   $192.40  
  7 purchase totals = $1,098.00       $1,196.8019   $1,196.79   $1,196.80   $1,196.80