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 $24.56   4.552%   $25.678   $25.68   $25.70   $25.70  
  Purchase #2 $99.48   10.591%   $110.0159   $110.02   $110.00   $110.00  
  Purchase #3 $49.49   6.568%   $52.7405   $52.74   $52.75   $52.70  
  Purchase #4 $208.37   12.257%   $233.9099   $233.91   $233.90   $233.90  
  Purchase #5 $74.85   10.768%   $82.9098   $82.91   $82.90   $82.90  
  Purchase #6 $164.90   8.524%   $178.9561   $178.96   $178.95   $179.00  
  Purchase #7 $45.47   10.117%   $50.0702   $50.07   $50.05   $50.10  
  7 purchase totals = $667.12       $734.2804   $734.29   $734.25   $734.30