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 $223.77   12.173%   $251.0095   $251.01   $251.00   $251.00  
  Purchase #2 $241.57   10.357%   $266.5894   $266.59   $266.60   $266.60  
  Purchase #3 $93.77   12.697%   $105.676   $105.68   $105.70   $105.70  
  Purchase #4 $70.35   12.169%   $78.9109   $78.91   $78.90   $78.90  
  Purchase #5 $184.99   8.847%   $201.3561   $201.36   $201.35   $201.40  
  Purchase #6 $99.92   13.362%   $113.2713   $113.27   $113.25   $113.30  
  Purchase #7 $38.30   12.316%   $43.017   $43.02   $43.00   $43.00  
  7 purchase totals = $952.67       $1,059.8302   $1,059.84   $1,059.80   $1,059.90