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 $250.38   4.251%   $261.0237   $261.02   $261.00   $261.00  
  Purchase #2 $202.69   8.367%   $219.6491   $219.65   $219.65   $219.60  
  Purchase #3 $100.82   5.776%   $106.6434   $106.64   $106.65   $106.60  
  Purchase #4 $232.39   8.350%   $251.7946   $251.79   $251.80   $251.80  
  Purchase #5 $142.77   5.313%   $150.3554   $150.36   $150.35   $150.40  
  Purchase #6 $49.34   13.800%   $56.1489   $56.15   $56.15   $56.10  
  Purchase #7 $114.64   6.652%   $122.2659   $122.27   $122.25   $122.30  
  7 purchase totals = $1,093.03       $1,167.8810   $1,167.88   $1,167.85   $1,167.80