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 $55.83   5.171%   $58.717   $58.72   $58.70   $58.70  
  Purchase #2 $45.83   6.151%   $48.649   $48.65   $48.65   $48.60  
  Purchase #3 $147.74   7.633%   $159.017   $159.02   $159.00   $159.00  
  Purchase #4 $135.32   9.232%   $147.8127   $147.81   $147.80   $147.80  
  Purchase #5 $117.55   13.653%   $133.5991   $133.60   $133.60   $133.60  
  Purchase #6 $168.43   9.128%   $183.8043   $183.80   $183.80   $183.80  
  Purchase #7 $208.37   6.790%   $222.5183   $222.52   $222.50   $222.50  
  7 purchase totals = $879.07       $954.1174   $954.12   $954.05   $954.00