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 $61.26   6.205%   $65.0612   $65.06   $65.05   $65.10  
  Purchase #2 $240.91   9.671%   $264.2084   $264.21   $264.20   $264.20  
  Purchase #3 $205.80   11.826%   $230.1379   $230.14   $230.15   $230.10  
  Purchase #4 $250.74   13.261%   $283.9906   $283.99   $284.00   $284.00  
  Purchase #5 $44.27   5.313%   $46.6221   $46.62   $46.60   $46.60  
  Purchase #6 $198.61   7.214%   $212.9377   $212.94   $212.95   $212.90  
  Purchase #7 $249.38   6.809%   $266.3603   $266.36   $266.35   $266.40  
  7 purchase totals = $1,250.97       $1,369.3182   $1,369.32   $1,369.30   $1,369.30