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 $22.34   13.661%   $25.3919   $25.39   $25.40   $25.40  
  Purchase #2 $65.98   4.809%   $69.153   $69.15   $69.15   $69.20  
  Purchase #3 $102.99   3.256%   $106.3434   $106.34   $106.35   $106.30  
  Purchase #4 $213.72   4.364%   $223.0467   $223.05   $223.05   $223.00  
  Purchase #5 $204.94   4.105%   $213.3528   $213.35   $213.35   $213.40  
  Purchase #6 $132.61   11.448%   $147.7912   $147.79   $147.80   $147.80  
  Purchase #7 $229.98   8.856%   $250.347   $250.35   $250.35   $250.30  
  7 purchase totals = $972.56       $1,035.4260   $1,035.42   $1,035.45   $1,035.40