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 $56.43   8.507%   $61.2305   $61.23   $61.25   $61.20  
  Purchase #2 $235.37   10.789%   $260.7641   $260.76   $260.75   $260.80  
  Purchase #3 $37.56   9.521%   $41.1361   $41.14   $41.15   $41.10  
  Purchase #4 $108.69   8.194%   $117.5961   $117.60   $117.60   $117.60  
  Purchase #5 $77.26   6.206%   $82.0548   $82.05   $82.05   $82.10  
  Purchase #6 $27.31   7.416%   $29.3353   $29.34   $29.35   $29.30  
  Purchase #7 $226.46   12.700%   $255.2204   $255.22   $255.20   $255.20  
  7 purchase totals = $769.08       $847.3373   $847.34   $847.35   $847.30