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 $207.52   13.209%   $234.9313   $234.93   $234.95   $234.90  
  Purchase #2 $154.27   4.127%   $160.6367   $160.64   $160.65   $160.60  
  Purchase #3 $158.90   8.806%   $172.8927   $172.89   $172.90   $172.90  
  Purchase #4 $203.51   6.367%   $216.4675   $216.47   $216.45   $216.50  
  Purchase #5 $222.79   8.301%   $241.2838   $241.28   $241.30   $241.30  
  Purchase #6 $209.95   4.627%   $219.6644   $219.66   $219.65   $219.70  
  Purchase #7 $75.25   4.556%   $78.6784   $78.68   $78.70   $78.70  
  7 purchase totals = $1,232.19       $1,324.5548   $1,324.55   $1,324.60   $1,324.60