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 $228.65   13.840%   $260.2952   $260.30   $260.30   $260.30  
  Purchase #2 $167.94   8.588%   $182.3627   $182.36   $182.35   $182.40  
  Purchase #3 $109.30   9.119%   $119.2671   $119.27   $119.25   $119.30  
  Purchase #4 $45.85   6.675%   $48.9105   $48.91   $48.90   $48.90  
  Purchase #5 $50.98   10.156%   $56.1575   $56.16   $56.15   $56.20  
  Purchase #6 $181.56   12.414%   $204.0989   $204.10   $204.10   $204.10  
  Purchase #7 $111.45   11.553%   $124.3258   $124.33   $124.35   $124.30  
  7 purchase totals = $895.73       $995.4177   $995.43   $995.40   $995.50