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 $46.42   12.399%   $52.1756   $52.18   $52.20   $52.20  
  Purchase #2 $196.95   7.335%   $211.3963   $211.40   $211.40   $211.40  
  Purchase #3 $30.30   3.510%   $31.3635   $31.36   $31.35   $31.40  
  Purchase #4 $192.57   13.237%   $218.0605   $218.06   $218.05   $218.10  
  Purchase #5 $92.78   9.605%   $101.6915   $101.69   $101.70   $101.70  
  Purchase #6 $78.69   6.826%   $84.0614   $84.06   $84.05   $84.10  
  Purchase #7 $201.62   13.124%   $228.0806   $228.08   $228.10   $228.10  
  7 purchase totals = $839.33       $926.8294   $926.83   $926.85   $927.00