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 $159.52   10.732%   $176.6397   $176.64   $176.65   $176.60  
  Purchase #2 $237.38   13.500%   $269.4263   $269.43   $269.45   $269.40  
  Purchase #3 $144.53   5.323%   $152.2233   $152.22   $152.20   $152.20  
  Purchase #4 $202.36   13.635%   $229.9518   $229.95   $229.95   $230.00  
  Purchase #5 $229.67   10.398%   $253.5511   $253.55   $253.55   $253.60  
  Purchase #6 $13.77   4.319%   $14.3647   $14.36   $14.35   $14.40  
  Purchase #7 $189.72   10.295%   $209.2517   $209.25   $209.25   $209.30  
  7 purchase totals = $1,176.95       $1,305.4086   $1,305.40   $1,305.40   $1,305.50