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 $206.67   12.581%   $232.6712   $232.67   $232.65   $232.70  
  Purchase #2 $65.57   7.573%   $70.5356   $70.54   $70.55   $70.50  
  Purchase #3 $49.75   7.238%   $53.3509   $53.35   $53.35   $53.40  
  Purchase #4 $116.80   3.379%   $120.7467   $120.75   $120.75   $120.70  
  Purchase #5 $235.96   13.808%   $268.5414   $268.54   $268.55   $268.50  
  Purchase #6 $101.83   11.376%   $113.4142   $113.41   $113.40   $113.40  
  Purchase #7 $166.51   4.497%   $173.998   $174.00   $174.00   $174.00  
  7 purchase totals = $943.09       $1,033.2580   $1,033.26   $1,033.25   $1,033.20