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 $146.52   11.694%   $163.654   $163.65   $163.65   $163.70  
  Purchase #2 $76.43   9.352%   $83.5777   $83.58   $83.60   $83.60  
  Purchase #3 $181.98   11.774%   $203.4063   $203.41   $203.40   $203.40  
  Purchase #4 $46.59   12.601%   $52.4608   $52.46   $52.45   $52.50  
  Purchase #5 $130.72   7.573%   $140.6194   $140.62   $140.60   $140.60  
  Purchase #6 $189.28   6.135%   $200.8923   $200.89   $200.90   $200.90  
  Purchase #7 $112.90   8.870%   $122.9142   $122.91   $122.90   $122.90  
  7 purchase totals = $884.42       $967.5247   $967.52   $967.50   $967.60