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 $46.36   12.731%   $52.2621   $52.26   $52.25   $52.30  
  Purchase #2 $247.78   9.514%   $271.3538   $271.35   $271.35   $271.40  
  Purchase #3 $38.93   5.166%   $40.9411   $40.94   $40.95   $40.90  
  Purchase #4 $168.75   7.842%   $181.9834   $181.98   $182.00   $182.00  
  Purchase #5 $160.71   10.588%   $177.726   $177.73   $177.75   $177.70  
  Purchase #6 $125.75   7.842%   $135.6113   $135.61   $135.60   $135.60  
  Purchase #7 $149.94   4.283%   $156.3619   $156.36   $156.35   $156.40  
  7 purchase totals = $938.22       $1,016.2396   $1,016.23   $1,016.25   $1,016.30