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 $227.47   6.157%   $241.4753   $241.48   $241.50   $241.50  
  Purchase #2 $244.78   8.488%   $265.5569   $265.56   $265.55   $265.60  
  Purchase #3 $180.65   11.231%   $200.9388   $200.94   $200.95   $200.90  
  Purchase #4 $237.51   7.313%   $254.8791   $254.88   $254.90   $254.90  
  Purchase #5 $62.93   3.515%   $65.142   $65.14   $65.15   $65.10  
  Purchase #6 $220.39   6.793%   $235.3611   $235.36   $235.35   $235.40  
  Purchase #7 $114.98   13.529%   $130.5356   $130.54   $130.55   $130.50  
  7 purchase totals = $1,288.71       $1,393.8888   $1,393.90   $1,393.95   $1,393.90