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 $184.96   6.251%   $196.5218   $196.52   $196.50   $196.50  
  Purchase #2 $132.36   9.276%   $144.6377   $144.64   $144.65   $144.60  
  Purchase #3 $121.83   11.138%   $135.3994   $135.40   $135.40   $135.40  
  Purchase #4 $59.66   6.664%   $63.6357   $63.64   $63.65   $63.60  
  Purchase #5 $122.97   11.251%   $136.8054   $136.81   $136.80   $136.80  
  Purchase #6 $240.52   5.616%   $254.0276   $254.03   $254.05   $254.00  
  Purchase #7 $121.72   9.450%   $133.2225   $133.22   $133.20   $133.20  
  7 purchase totals = $984.02       $1,064.2501   $1,064.26   $1,064.25   $1,064.10