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 $66.88   5.466%   $70.5357   $70.54   $70.55   $70.50  
  Purchase #2 $102.40   3.176%   $105.6522   $105.65   $105.65   $105.70  
  Purchase #3 $14.81   11.783%   $16.5551   $16.56   $16.55   $16.60  
  Purchase #4 $138.95   9.425%   $152.046   $152.05   $152.05   $152.00  
  Purchase #5 $71.53   3.144%   $73.7789   $73.78   $73.80   $73.80  
  Purchase #6 $218.88   4.644%   $229.0448   $229.04   $229.05   $229.00  
  Purchase #7 $99.99   9.338%   $109.3271   $109.33   $109.35   $109.30  
  7 purchase totals = $713.44       $756.9398   $756.95   $757.00   $756.90