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 $86.59   7.864%   $93.3994   $93.40   $93.40   $93.40  
  Purchase #2 $184.60   3.611%   $191.2659   $191.27   $191.25   $191.30  
  Purchase #3 $63.50   10.307%   $70.0449   $70.04   $70.05   $70.00  
  Purchase #4 $74.53   9.403%   $81.5381   $81.54   $81.55   $81.50  
  Purchase #5 $159.27   5.177%   $167.5154   $167.52   $167.50   $167.50  
  Purchase #6 $176.81   5.449%   $186.4444   $186.44   $186.45   $186.40  
  Purchase #7 $238.62   13.342%   $270.4567   $270.46   $270.45   $270.50  
  7 purchase totals = $983.92       $1,060.6648   $1,060.67   $1,060.65   $1,060.60