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 $206.32   12.801%   $232.731   $232.73   $232.75   $232.70  
  Purchase #2 $86.92   6.858%   $92.881   $92.88   $92.90   $92.90  
  Purchase #3 $221.96   7.646%   $238.9311   $238.93   $238.95   $238.90  
  Purchase #4 $157.57   8.296%   $170.642   $170.64   $170.65   $170.60  
  Purchase #5 $58.65   13.400%   $66.5091   $66.51   $66.50   $66.50  
  Purchase #6 $24.37   10.710%   $26.98   $26.98   $27.00   $27.00  
  Purchase #7 $150.45   3.740%   $156.0768   $156.08   $156.10   $156.10  
  7 purchase totals = $906.24       $984.7510   $984.75   $984.85   $984.70