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 $67.93   4.768%   $71.1689   $71.17   $71.15   $71.20  
  Purchase #2 $220.36   6.652%   $235.0183   $235.02   $235.00   $235.00  
  Purchase #3 $60.26   10.393%   $66.5228   $66.52   $66.50   $66.50  
  Purchase #4 $166.35   8.590%   $180.6395   $180.64   $180.65   $180.60  
  Purchase #5 $35.53   4.782%   $37.229   $37.23   $37.25   $37.20  
  Purchase #6 $22.30   9.199%   $24.3514   $24.35   $24.35   $24.40  
  Purchase #7 $223.54   3.556%   $231.4891   $231.49   $231.50   $231.50  
  7 purchase totals = $796.27       $846.4190   $846.42   $846.40   $846.40