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 $46.29   5.751%   $48.9521   $48.95   $48.95   $49.00  
  Purchase #2 $237.60   11.564%   $265.0761   $265.08   $265.10   $265.10  
  Purchase #3 $133.65   3.294%   $138.0524   $138.05   $138.05   $138.10  
  Purchase #4 $172.87   11.224%   $192.2729   $192.27   $192.25   $192.30  
  Purchase #5 $186.39   3.198%   $192.3508   $192.35   $192.35   $192.40  
  Purchase #6 $124.95   12.271%   $140.2826   $140.28   $140.30   $140.30  
  Purchase #7 $46.47   8.852%   $50.5835   $50.58   $50.60   $50.60  
  7 purchase totals = $948.22       $1,027.5704   $1,027.56   $1,027.60   $1,027.80