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 $48.86   13.779%   $55.5924   $55.59   $55.60   $55.60  
  Purchase #2 $163.43   8.643%   $177.5553   $177.56   $177.55   $177.60  
  Purchase #3 $186.90   12.286%   $209.8625   $209.86   $209.85   $209.90  
  Purchase #4 $26.31   11.284%   $29.2788   $29.28   $29.30   $29.30  
  Purchase #5 $83.66   11.670%   $93.4231   $93.42   $93.40   $93.40  
  Purchase #6 $219.72   6.541%   $234.0919   $234.09   $234.10   $234.10  
  Purchase #7 $212.57   13.711%   $241.7155   $241.72   $241.70   $241.70  
  7 purchase totals = $941.45       $1,041.5195   $1,041.52   $1,041.50   $1,041.60