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 $61.28   3.476%   $63.4101   $63.41   $63.40   $63.40  
  Purchase #2 $205.80   12.735%   $232.0086   $232.01   $232.00   $232.00  
  Purchase #3 $186.27   8.661%   $202.4028   $202.40   $202.40   $202.40  
  Purchase #4 $99.30   13.495%   $112.7005   $112.70   $112.70   $112.70  
  Purchase #5 $179.70   13.222%   $203.4599   $203.46   $203.45   $203.50  
  Purchase #6 $9.28   4.283%   $9.6775   $9.68   $9.70   $9.70  
  Purchase #7 $108.93   12.766%   $122.836   $122.84   $122.85   $122.80  
  7 purchase totals = $850.56       $946.4954   $946.50   $946.50   $946.50