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 $125.88   6.690%   $134.3014   $134.30   $134.30   $134.30  
  Purchase #2 $182.37   10.666%   $201.8216   $201.82   $201.80   $201.80  
  Purchase #3 $11.50   13.222%   $13.0205   $13.02   $13.00   $13.00  
  Purchase #4 $147.89   12.575%   $166.4872   $166.49   $166.50   $166.50  
  Purchase #5 $53.79   5.261%   $56.6199   $56.62   $56.60   $56.60  
  Purchase #6 $177.72   8.631%   $193.059   $193.06   $193.05   $193.10  
  Purchase #7 $199.94   6.174%   $212.2843   $212.28   $212.30   $212.30  
  7 purchase totals = $899.09       $977.5939   $977.59   $977.55   $977.60