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 $93.49   3.727%   $96.9744   $96.97   $96.95   $97.00  
  Purchase #2 $35.28   9.403%   $38.5974   $38.60   $38.60   $38.60  
  Purchase #3 $127.67   5.164%   $134.2629   $134.26   $134.25   $134.30  
  Purchase #4 $231.82   9.560%   $253.982   $253.98   $254.00   $254.00  
  Purchase #5 $210.79   12.851%   $237.8786   $237.88   $237.90   $237.90  
  Purchase #6 $111.96   12.562%   $126.0244   $126.02   $126.00   $126.00  
  Purchase #7 $163.93   12.710%   $184.7655   $184.77   $184.75   $184.80  
  7 purchase totals = $974.94       $1,072.4852   $1,072.48   $1,072.45   $1,072.60