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 $222.89   11.412%   $248.3262   $248.33   $248.35   $248.30  
  Purchase #2 $123.72   10.610%   $136.8467   $136.85   $136.85   $136.80  
  Purchase #3 $100.57   5.698%   $106.3005   $106.30   $106.30   $106.30  
  Purchase #4 $72.67   9.629%   $79.6674   $79.67   $79.65   $79.70  
  Purchase #5 $22.92   9.284%   $25.0479   $25.05   $25.05   $25.00  
  Purchase #6 $240.72   13.674%   $273.6361   $273.64   $273.65   $273.60  
  Purchase #7 $113.50   9.758%   $124.5753   $124.58   $124.60   $124.60  
  7 purchase totals = $896.99       $994.4001   $994.42   $994.45   $994.30