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 $177.47   13.393%   $201.2386   $201.24   $201.25   $201.20  
  Purchase #2 $200.50   12.574%   $225.7109   $225.71   $225.70   $225.70  
  Purchase #3 $145.78   4.253%   $151.98   $151.98   $152.00   $152.00  
  Purchase #4 $234.25   10.653%   $259.2047   $259.20   $259.20   $259.20  
  Purchase #5 $29.65   11.602%   $33.09   $33.09   $33.10   $33.10  
  Purchase #6 $216.80   8.578%   $235.3971   $235.40   $235.40   $235.40  
  Purchase #7 $173.80   13.731%   $197.6645   $197.66   $197.65   $197.70  
  7 purchase totals = $1,178.25       $1,304.2858   $1,304.28   $1,304.30   $1,304.30