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 $169.61   10.148%   $186.822   $186.82   $186.80   $186.80  
  Purchase #2 $71.78   8.599%   $77.9524   $77.95   $77.95   $78.00  
  Purchase #3 $132.44   8.300%   $143.4325   $143.43   $143.45   $143.40  
  Purchase #4 $201.86   11.566%   $225.2071   $225.21   $225.20   $225.20  
  Purchase #5 $50.81   3.378%   $52.5264   $52.53   $52.55   $52.50  
  Purchase #6 $193.81   13.617%   $220.2011   $220.20   $220.20   $220.20  
  Purchase #7 $115.54   9.181%   $126.1477   $126.15   $126.15   $126.10  
  7 purchase totals = $935.85       $1,032.2892   $1,032.29   $1,032.30   $1,032.20