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 $57.46   9.643%   $63.0009   $63.00   $63.00   $63.00  
  Purchase #2 $147.29   12.754%   $166.0754   $166.08   $166.10   $166.10  
  Purchase #3 $202.68   6.293%   $215.4347   $215.43   $215.45   $215.40  
  Purchase #4 $54.90   12.185%   $61.5896   $61.59   $61.60   $61.60  
  Purchase #5 $68.55   12.794%   $77.3203   $77.32   $77.30   $77.30  
  Purchase #6 $231.30   6.837%   $247.114   $247.11   $247.10   $247.10  
  Purchase #7 $103.67   4.619%   $108.4585   $108.46   $108.45   $108.50  
  7 purchase totals = $865.85       $938.9934   $938.99   $939.00   $939.00