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 $166.25   13.855%   $189.2839   $189.28   $189.30   $189.30  
  Purchase #2 $228.76   12.191%   $256.6481   $256.65   $256.65   $256.60  
  Purchase #3 $151.60   3.292%   $156.5907   $156.59   $156.60   $156.60  
  Purchase #4 $216.78   5.456%   $228.6075   $228.61   $228.60   $228.60  
  Purchase #5 $64.99   13.342%   $73.661   $73.66   $73.65   $73.70  
  Purchase #6 $207.72   13.785%   $236.3542   $236.35   $236.35   $236.40  
  Purchase #7 $135.29   4.778%   $141.7542   $141.75   $141.75   $141.80  
  7 purchase totals = $1,171.39       $1,282.8996   $1,282.89   $1,282.90   $1,283.00