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 $244.46   8.416%   $265.0338   $265.03   $265.05   $265.00  
  Purchase #2 $32.55   12.581%   $36.6451   $36.65   $36.65   $36.60  
  Purchase #3 $77.91   8.532%   $84.5573   $84.56   $84.55   $84.60  
  Purchase #4 $36.91   6.545%   $39.3258   $39.33   $39.35   $39.30  
  Purchase #5 $176.34   12.276%   $197.9875   $197.99   $198.00   $198.00  
  Purchase #6 $228.85   6.364%   $243.414   $243.41   $243.40   $243.40  
  Purchase #7 $101.92   9.699%   $111.8052   $111.81   $111.80   $111.80  
  7 purchase totals = $898.94       $978.7687   $978.78   $978.80   $978.70