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 $205.37   6.442%   $218.5999   $218.60   $218.60   $218.60  
  Purchase #2 $229.85   6.434%   $244.6385   $244.64   $244.65   $244.60  
  Purchase #3 $9.46   11.314%   $10.5303   $10.53   $10.55   $10.50  
  Purchase #4 $51.85   11.592%   $57.8605   $57.86   $57.85   $57.90  
  Purchase #5 $124.25   3.561%   $128.6745   $128.67   $128.65   $128.70  
  Purchase #6 $193.25   12.798%   $217.9821   $217.98   $218.00   $218.00  
  Purchase #7 $223.43   10.363%   $246.5841   $246.58   $246.60   $246.60  
  7 purchase totals = $1,037.46       $1,124.8699   $1,124.86   $1,124.90   $1,124.90