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 $91.41   7.520%   $98.284   $98.28   $98.30   $98.30  
  Purchase #2 $123.61   7.446%   $132.814   $132.81   $132.80   $132.80  
  Purchase #3 $50.37   10.589%   $55.7037   $55.70   $55.70   $55.70  
  Purchase #4 $34.27   8.771%   $37.2758   $37.28   $37.30   $37.30  
  Purchase #5 $112.77   9.534%   $123.5215   $123.52   $123.50   $123.50  
  Purchase #6 $189.46   7.399%   $203.4781   $203.48   $203.50   $203.50  
  Purchase #7 $221.87   10.473%   $245.1064   $245.11   $245.10   $245.10  
  7 purchase totals = $823.76       $896.1835   $896.18   $896.20   $896.20