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 $56.94   9.276%   $62.2218   $62.22   $62.20   $62.20  
  Purchase #2 $81.72   5.864%   $86.5121   $86.51   $86.50   $86.50  
  Purchase #3 $198.90   13.626%   $226.0021   $226.00   $226.00   $226.00  
  Purchase #4 $142.51   3.835%   $147.9753   $147.98   $148.00   $148.00  
  Purchase #5 $166.79   7.435%   $179.1908   $179.19   $179.20   $179.20  
  Purchase #6 $151.69   9.231%   $165.6925   $165.69   $165.70   $165.70  
  Purchase #7 $56.67   3.558%   $58.6863   $58.69   $58.70   $58.70  
  7 purchase totals = $855.22       $926.2809   $926.28   $926.30   $926.30