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 $244.36   7.841%   $263.5203   $263.52   $263.50   $263.50  
  Purchase #2 $120.50   8.618%   $130.8847   $130.88   $130.90   $130.90  
  Purchase #3 $159.63   6.460%   $169.9421   $169.94   $169.95   $169.90  
  Purchase #4 $7.93   6.809%   $8.47   $8.47   $8.45   $8.50  
  Purchase #5 $101.41   12.511%   $114.0974   $114.10   $114.10   $114.10  
  Purchase #6 $106.56   4.770%   $111.6429   $111.64   $111.65   $111.60  
  Purchase #7 $207.81   8.320%   $225.0998   $225.10   $225.10   $225.10  
  7 purchase totals = $948.20       $1,023.6572   $1,023.65   $1,023.65   $1,023.60