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 $58.43   8.387%   $63.3305   $63.33   $63.35   $63.30  
  Purchase #2 $109.55   11.580%   $122.2359   $122.24   $122.25   $122.20  
  Purchase #3 $102.55   6.270%   $108.9799   $108.98   $109.00   $109.00  
  Purchase #4 $211.25   4.169%   $220.057   $220.06   $220.05   $220.10  
  Purchase #5 $26.85   4.868%   $28.1571   $28.16   $28.15   $28.20  
  Purchase #6 $14.62   5.752%   $15.4609   $15.46   $15.45   $15.50  
  Purchase #7 $164.98   10.767%   $182.7434   $182.74   $182.75   $182.70  
  7 purchase totals = $688.23       $740.9647   $740.97   $741.00   $741.00