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 $240.68   10.770%   $266.6012   $266.60   $266.60   $266.60  
  Purchase #2 $125.44   3.557%   $129.9019   $129.90   $129.90   $129.90  
  Purchase #3 $94.96   9.249%   $103.7429   $103.74   $103.75   $103.70  
  Purchase #4 $80.53   7.516%   $86.5826   $86.58   $86.60   $86.60  
  Purchase #5 $193.33   3.601%   $200.2918   $200.29   $200.30   $200.30  
  Purchase #6 $55.96   12.601%   $63.0115   $63.01   $63.00   $63.00  
  Purchase #7 $221.32   10.428%   $244.3992   $244.40   $244.40   $244.40  
  7 purchase totals = $1,012.22       $1,094.5311   $1,094.52   $1,094.55   $1,094.50