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 $85.63   9.639%   $93.8839   $93.88   $93.90   $93.90  
  Purchase #2 $246.72   11.590%   $275.3148   $275.31   $275.30   $275.30  
  Purchase #3 $232.78   6.651%   $248.2622   $248.26   $248.25   $248.30  
  Purchase #4 $153.67   6.421%   $163.5372   $163.54   $163.55   $163.50  
  Purchase #5 $184.25   9.821%   $202.3452   $202.35   $202.35   $202.30  
  Purchase #6 $165.28   6.832%   $176.5719   $176.57   $176.55   $176.60  
  Purchase #7 $226.41   13.241%   $256.3889   $256.39   $256.40   $256.40  
  7 purchase totals = $1,294.74       $1,416.3041   $1,416.30   $1,416.30   $1,416.30