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 $141.46   7.687%   $152.334   $152.33   $152.35   $152.30  
  Purchase #2 $120.76   11.553%   $134.7114   $134.71   $134.70   $134.70  
  Purchase #3 $182.70   11.645%   $203.9754   $203.98   $204.00   $204.00  
  Purchase #4 $235.25   12.756%   $265.2585   $265.26   $265.25   $265.30  
  Purchase #5 $154.43   13.566%   $175.38   $175.38   $175.40   $175.40  
  Purchase #6 $32.70   9.382%   $35.7679   $35.77   $35.75   $35.80  
  Purchase #7 $59.64   8.310%   $64.5961   $64.60   $64.60   $64.60  
  7 purchase totals = $926.94       $1,032.0233   $1,032.03   $1,032.05   $1,032.10