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 $56.56   12.323%   $63.5299   $63.53   $63.55   $63.50  
  Purchase #2 $208.90   12.731%   $235.4951   $235.50   $235.50   $235.50  
  Purchase #3 $36.66   9.146%   $40.0129   $40.01   $40.00   $40.00  
  Purchase #4 $71.57   12.340%   $80.4017   $80.40   $80.40   $80.40  
  Purchase #5 $51.74   8.319%   $56.0443   $56.04   $56.05   $56.00  
  Purchase #6 $47.81   6.351%   $50.8464   $50.85   $50.85   $50.80  
  Purchase #7 $163.28   6.341%   $173.6336   $173.63   $173.65   $173.60  
  7 purchase totals = $636.52       $699.9639   $699.96   $700.00   $699.80