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 $209.95   12.656%   $236.5213   $236.52   $236.50   $236.50  
  Purchase #2 $87.50   9.630%   $95.9263   $95.93   $95.95   $95.90  
  Purchase #3 $247.81   5.156%   $260.5871   $260.59   $260.60   $260.60  
  Purchase #4 $49.65   5.351%   $52.3068   $52.31   $52.30   $52.30  
  Purchase #5 $149.94   7.247%   $160.8062   $160.81   $160.80   $160.80  
  Purchase #6 $133.50   7.830%   $143.9531   $143.95   $143.95   $144.00  
  Purchase #7 $200.69   12.460%   $225.696   $225.70   $225.70   $225.70  
  7 purchase totals = $1,079.04       $1,175.7968   $1,175.81   $1,175.80   $1,175.80