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 $231.89   5.432%   $244.4863   $244.49   $244.50   $244.50  
  Purchase #2 $16.61   11.352%   $18.4956   $18.50   $18.50   $18.50  
  Purchase #3 $138.72   12.705%   $156.3444   $156.34   $156.35   $156.30  
  Purchase #4 $138.88   7.477%   $149.2641   $149.26   $149.25   $149.30  
  Purchase #5 $173.62   4.225%   $180.9554   $180.96   $180.95   $181.00  
  Purchase #6 $231.83   3.601%   $240.1782   $240.18   $240.20   $240.20  
  Purchase #7 $96.87   3.544%   $100.3031   $100.30   $100.30   $100.30  
  7 purchase totals = $1,028.42       $1,090.0271   $1,090.03   $1,090.05   $1,090.10