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 $84.91   12.803%   $95.781   $95.78   $95.80   $95.80  
  Purchase #2 $34.30   12.781%   $38.6839   $38.68   $38.70   $38.70  
  Purchase #3 $144.27   6.330%   $153.4023   $153.40   $153.40   $153.40  
  Purchase #4 $54.52   11.321%   $60.6922   $60.69   $60.70   $60.70  
  Purchase #5 $112.41   13.605%   $127.7034   $127.70   $127.70   $127.70  
  Purchase #6 $111.73   9.341%   $122.1667   $122.17   $122.15   $122.20  
  Purchase #7 $200.88   12.511%   $226.0121   $226.01   $226.00   $226.00  
  7 purchase totals = $743.02       $824.4416   $824.43   $824.45   $824.50