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 $144.98   6.616%   $154.5719   $154.57   $154.55   $154.60  
  Purchase #2 $148.71   12.845%   $167.8118   $167.81   $167.80   $167.80  
  Purchase #3 $60.99   13.421%   $69.1755   $69.18   $69.20   $69.20  
  Purchase #4 $111.55   5.264%   $117.422   $117.42   $117.40   $117.40  
  Purchase #5 $232.41   3.319%   $240.1237   $240.12   $240.10   $240.10  
  Purchase #6 $82.94   4.777%   $86.902   $86.90   $86.90   $86.90  
  Purchase #7 $210.25   6.872%   $224.6984   $224.70   $224.70   $224.70  
  7 purchase totals = $991.83       $1,060.7053   $1,060.70   $1,060.65   $1,060.70